Trial Outcomes & Findings for Dose Ranging Study of ALX-0171 in Infants Hospitalized for Respiratory Syncytial Virus Lower Respiratory Tract Infection (NCT NCT02979431)

Last Updated: 2019-10-18

Results Overview

The primary endpoint for this trial was the time needed for the viral load to drop below the quantification limit (time-to-BQL) of the plaque assay in nasal mid-turbinate swab specimens. Time-to-BQL was defined as the time from the first study drug administration to the first occurrence of a value below the quantification limit (BQL), provided the next measured value was also below the limit of quantification. The time to BQL for subjects with missing data and/or who did not reach BQL during the trial were censored at the last non-missing viral load assessment. The primary endpoint was analysed using logrank test to compare time-to-BQL between each of the ALX-0171 treatment groups and the combined placebo group. The tests were performed in a sequential way to preserve the family-wise error rate at 0.05. The comparisons were performed in the following order: ALX-0171 9 mg/kg vs Placebo, followed by ALX-0171 6mg/kg vs Placebo, ALX-0171 3mg/kg vs Placebo.

Recruitment status

COMPLETED

Study phase

PHASE2

Target enrollment

180 participants

Primary outcome timeframe

Overall Study Period (i.e., approximately 28 days)

Results posted on

2019-10-18

Participant Flow

A total of 301 subjects were screened.180 subjects were randomized to receive ALX-0171 3.0 mg/kg, ALX-0171 6.0 mg/kg, ALX-0171 9.0 mg/kg or placebo, yielding an overall allocation ratio of 3:1 active to placebo.

Participant milestones

Participant milestones
Measure	Placebo Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Overall Study STARTED	44	46	45	45
Overall Study Included in the mITT Population	42	45	43	45
Overall Study Included in the Safety Population	40	45	44	46
Overall Study COMPLETED	40	44	43	44
Overall Study NOT COMPLETED	4	2	2	1

Reasons for withdrawal

Reasons for withdrawal
Measure	Placebo Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Overall Study Parent/guardian withdrew consent	2	1	1	1
Overall Study Randomized but received no study drug	1	1	0	0
Overall Study Adverse Event	0	0	1	0
Overall Study Subject left country after Day14	1	0	0	0

Baseline Characteristics

modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).

Baseline characteristics by cohort

Baseline characteristics by cohort
Measure	Placebo n=42 Participants Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg n=45 Participants Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg n=43 Participants Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg n=45 Participants Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days	Total n=175 Participants Total of all reporting groups
Age, Categorical <=18 years	42 Participants n=93 Participants	45 Participants n=4 Participants	43 Participants n=27 Participants	45 Participants n=483 Participants	175 Participants n=36 Participants
Age, Categorical Between 18 and 65 years	0 Participants n=93 Participants	0 Participants n=4 Participants	0 Participants n=27 Participants	0 Participants n=483 Participants	0 Participants n=36 Participants
Age, Categorical >=65 years	0 Participants n=93 Participants	0 Participants n=4 Participants	0 Participants n=27 Participants	0 Participants n=483 Participants	0 Participants n=36 Participants
Age, Continuous	6.964 months STANDARD_DEVIATION 6.0668 • n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	6.933 months STANDARD_DEVIATION 5.8827 • n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	6.657 months STANDARD_DEVIATION 6.2605 • n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	7.022 months STANDARD_DEVIATION 5.6884 • n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	6.896 months STANDARD_DEVIATION 5.9234 • n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Age, Customized Age categories · < 6 months	24 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	23 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	27 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	25 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	99 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Age, Customized Age categories · ≥ 6 months and < 12 months	8 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	13 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	7 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	12 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	40 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Age, Customized Age categories · ≥ 12 months	10 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	9 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	9 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	8 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	36 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Age, Customized Gestational Age	38.5 Weeks STANDARD_DEVIATION 1.78 • n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	38.6 Weeks STANDARD_DEVIATION 1.99 • n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	38.6 Weeks STANDARD_DEVIATION 1.62 • n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	38.3 Weeks STANDARD_DEVIATION 1.54 • n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	38.5 Weeks STANDARD_DEVIATION 1.73 • n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Sex: Female, Male Female	24 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	15 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	19 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	17 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	75 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Sex: Female, Male Male	18 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	30 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	24 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	28 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	100 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Ethnicity (NIH/OMB) Hispanic or Latino	4 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	4 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	5 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	5 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	18 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Ethnicity (NIH/OMB) Not Hispanic or Latino	38 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	41 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	38 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	40 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	157 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Ethnicity (NIH/OMB) Unknown or Not Reported	0 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Race/Ethnicity, Customized Race · Asian	7 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	7 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	3 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	10 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	27 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Race/Ethnicity, Customized Race · Black or African American	0 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	1 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	1 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Race/Ethnicity, Customized Race · Multiple	0 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	2 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	2 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Race/Ethnicity, Customized Race · Other	0 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	1 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	3 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	4 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Race/Ethnicity, Customized Race · White	35 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	38 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	36 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	32 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	141 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Belgium	2 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	3 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	3 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	1 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	9 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Bulgaria	7 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	8 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	6 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	11 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	32 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Chile	0 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	4 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	4 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Colombia	0 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	1 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	1 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Croatia	6 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	6 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	8 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	3 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	23 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Germany	1 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	3 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	2 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	6 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Hungary	7 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	6 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	8 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	4 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	25 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Israel	0 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	2 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	1 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	1 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	4 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Latvia	2 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	1 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	2 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	5 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	10 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Malaysia	4 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	4 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	3 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	3 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	14 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Philippines	1 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	1 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	3 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	5 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Poland	5 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	5 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	3 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	13 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Slovakia	0 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	0 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	2 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	2 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	4 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Spain	5 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	7 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	2 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	1 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	15 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Region of Enrollment Thailand	2 Participants n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	2 Participants n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	1 Participants n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	5 Participants n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	10 Participants n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Number of days between symtpom onset and the first dose of study drug	3.16 days STANDARD_DEVIATION 1.207 • n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	3.34 days STANDARD_DEVIATION 1.144 • n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	3.23 days STANDARD_DEVIATION 0.845 • n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	3.25 days STANDARD_DEVIATION 1.149 • n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	3.25 days STANDARD_DEVIATION 1.088 • n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Global Severity Score (GSS)	9.1 score on a scale STANDARD_DEVIATION 2.44 • n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	9.2 score on a scale STANDARD_DEVIATION 2.00 • n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	9.3 score on a scale STANDARD_DEVIATION 2.09 • n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	9.4 score on a scale STANDARD_DEVIATION 2.41 • n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	9.2 score on a scale STANDARD_DEVIATION 2.23 • n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Respiratory Distress Instrument (RDAI)	8.5 score on a scale STANDARD_DEVIATION 3.74 • n=93 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	8.41 score on a scale STANDARD_DEVIATION 4.07 • n=4 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	8.74 score on a scale STANDARD_DEVIATION 3.19 • n=27 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	8.11 score on a scale STANDARD_DEVIATION 3.80 • n=483 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).	8.44 score on a scale STANDARD_DEVIATION 3.693 • n=36 Participants • modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).
Height	65.84 centimetres STANDARD_DEVIATION 9.997 • n=93 Participants	65.71 centimetres STANDARD_DEVIATION 10.210 • n=4 Participants	65.25 centimetres STANDARD_DEVIATION 10.190 • n=27 Participants	66.55 centimetres STANDARD_DEVIATION 9.580 • n=483 Participants	65.85 centimetres STANDARD_DEVIATION 9.915 • n=36 Participants
Weight	7.065 kilograms STANDARD_DEVIATION 2.4193 • n=93 Participants	7.188 kilograms STANDARD_DEVIATION 2.2278 • n=4 Participants	6.988 kilograms STANDARD_DEVIATION 2.4084 • n=27 Participants	7.020 kilograms STANDARD_DEVIATION 2.2474 • n=483 Participants	7.066 kilograms STANDARD_DEVIATION 2.3059 • n=36 Participants
Weight category ≥ 3.0 kg and < 4.0 kg	1 Participants n=93 Participants	2 Participants n=4 Participants	0 Participants n=27 Participants	2 Participants n=483 Participants	5 Participants n=36 Participants
Weight category ≥ 4.0 kg and < 5.0 kg	8 Participants n=93 Participants	6 Participants n=4 Participants	13 Participants n=27 Participants	7 Participants n=483 Participants	34 Participants n=36 Participants
Weight category ≥ 5.0 kg and < 7.0 kg	15 Participants n=93 Participants	15 Participants n=4 Participants	11 Participants n=27 Participants	14 Participants n=483 Participants	55 Participants n=36 Participants
Weight category ≥ 7.0 kg and < 10.0 kg	11 Participants n=93 Participants	17 Participants n=4 Participants	12 Participants n=27 Participants	19 Participants n=483 Participants	59 Participants n=36 Participants
Weight category ≥ 10.0 kg and < 12.0 kg	6 Participants n=93 Participants	4 Participants n=4 Participants	7 Participants n=27 Participants	1 Participants n=483 Participants	18 Participants n=36 Participants
Weight category ≥ 12.0 kg and < 15.0 kg	1 Participants n=93 Participants	1 Participants n=4 Participants	0 Participants n=27 Participants	2 Participants n=483 Participants	4 Participants n=36 Participants

PRIMARY outcome

Timeframe: Overall Study Period (i.e., approximately 28 days)

Population: modified Intent-to-Treat Population (mITT): All randomized subjects who received at least 1 study drug administration. In this population, the subjects were classified as randomized (i.e.,using the treatment to which the subject was randomized).

Outcome measures

Outcome measures
Measure	Placebo n=42 Participants Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg n=45 Participants Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg n=43 Participants Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg n=45 Participants Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Time for Viral Load to Drop Below Assay Quantification Limit (BQL) (Plaque Assay Analysis)	46.1 hours Interval 29.33 to 94.42	14.2 hours Interval 5.17 to 26.28	5.1 hours Interval 4.78 to 24.72	5.1 hours Interval 4.97 to 5.17

SECONDARY outcome

Timeframe: from Baseline untill Day 2 (5 hours post-dose)

A formal comparison for change from Baseline in GSS to Day 2, 5 hours post-dose was performed using a contrast analysis on a longitudinal mixed model with random factor subject and fixed effects baseline value, treatment group and timepoint, including the treatment-by-timepoint interaction term. All data up to and including Day 3 were used in the longitudinal mixed model. The Kenward-Roger approximation of degrees of freedom was used. The model was fitted using an unstructured variance-covariance matrix. The individual pair-wise comparisons were reported (comparison in least square \[LS\] means for 9.0 mg/kg versus placebo; 6.0mg/kg versus placebo; 3.0 mg/kg versus placebo). Evolution over time in Global Severity Score. The maximum total score is 20 (minimum:0 to manimum:20); higher score indicates more severe disease.

Outcome measures

Outcome measures
Measure	Placebo n=42 Participants Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg n=45 Participants Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg n=43 Participants Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg n=45 Participants Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Change From Baseline in Global Severity Score on Day 2 (5 Hours Post-dose)	-3.6392 score on a scale Standard Error 0.4160	-3.8548 score on a scale Standard Error 0.4103	-4.1296 score on a scale Standard Error 0.4129	-4.2844 score on a scale Standard Error 0.4099

SECONDARY outcome

Timeframe: Overall Study Period (i.e., approximately 28 days)

The time-to-clinical response was defined as the time between the first study drug administration and the time of achieving adequate oxygen saturation (defined as SpO2 \> 92% over a period of at least 4 hours) and adequate oral feeding (which is sufficient to maintain sufficient hydration, in the judgment of the Investigator).

Outcome measures

Outcome measures
Measure	Placebo n=42 Participants Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg n=45 Participants Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg n=43 Participants Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg n=45 Participants Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Time-to-Clinical Response Time-to-Clinical Response	47.9 hours Interval 29.17 to 64.08	44.1 hours Interval 28.33 to 51.2	27.9 hours Interval 21.08 to 43.68	46.3 hours Interval 38.0 to 50.38
Time-to-Clinical Response Time-to-adequate oral feeding	43.7 hours Interval 22.5 to 47.58	44.0 hours Interval 25.92 to 52.0	17.6 hours Interval 6.5 to 25.85	23.8 hours Interval 17.17 to 38.0
Time-to-Clinical Response Time-to-adequate oxygen saturation	53.4 hours Interval 28.7 to 71.78	38.5 hours Interval 24.75 to 61.93	29.5 hours Interval 20.75 to 47.43	46.5 hours Interval 42.15 to 48.25

SECONDARY outcome

Timeframe: Overall Study Period (i.e., approximately 28 days)

Population: The modified ITT (mITT) population consisted of all randomized subjects who received at least 1 administration of study drug. When using this population, the subjects were classified as randomized (i.e., using the treatment to which the subject was randomized).

As secondary endpoint, the time-to-BQL using RT-qPCR was summarized using Kaplan Meier (KM) estimates. No p-values were calculated. For RSV load by RT-qPCR, the lower limit of quantification (LLOQ) was 2.4 log10 copies/mL. The upper limit confidence interval (CI) could not be calculated; Values of the 25 percentile are reported here.

Outcome measures

Outcome measures
Measure	Placebo n=42 Participants Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg n=45 Participants Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg n=43 Participants Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg n=45 Participants Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Time-to-BQL (RT-qPCR)	26.7 hours Interval 5.0 to 49.92	26.8 hours Interval 5.17 to 44.62	28.9 hours Interval 18.25 to 49.25	6.3 hours Interval 4.97 to 25.25

SECONDARY outcome

Timeframe: Overall Study Period (i.e., approximately 28 days)

Population: RSV-Infected Population: A central RSV test was used for defining the RSV-Infected population. The RSV-Infected population consisted of all randomized subjects with RSV infection, as confirmed by RT-qPCR (hVIVO quantitative PCR assay) on Day 1 (pre- or post-dose), who received at least 1 administration of study drug.

The time-to-undetectability (hours), defined as the time from the first study drug administration to the first occurrence of viral titer below the lower limit of quantification (LLOQ), and target not detected provided the next measured value was also below the quantification limit and undetected, were summarized using KM estimates, based on the plaque assay. The time-to-event for subjects with missing data and/or subjects who did not reach undetectability during the trial were censored at the last non-missing viral load assessment. For RSV load by plaque assay the LLOQ was 1.7 log10 pfu/mL.

Outcome measures

Outcome measures
Measure	Placebo n=35 Participants Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg n=40 Participants Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg n=40 Participants Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg n=38 Participants Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Time-to-undetectable Viral Load (Plaque Assay Analysis)	95.9 hours Interval 47.23 to 121.82	26.3 hours Interval 20.25 to 28.92	21.0 hours Interval 4.88 to 28.25	5.1 hours Interval 5.0 to 5.87

SECONDARY outcome

Timeframe: From Baseline until Day 14 (Follow-up) (Baseline; Day 1, 5 hours post-dose; Day 3, 2 hours post-dose; and Follow-up reported)

Change from Baseline in RSV Load measured by Plaque Assay (RSV Infected Population)

Outcome measures

Outcome measures
Measure	Placebo n=35 Participants Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg n=40 Participants Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg n=40 Participants Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg n=38 Participants Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Viral Load Changes From Baseline (Plaque Assay Analysis) Baseline	3.494 log10 pfu/mL Standard Error 0.2396	3.312 log10 pfu/mL Standard Error 0.2165	3.135 log10 pfu/mL Standard Error 0.2430	2.385 log10 pfu/mL Standard Error 0.2526
Viral Load Changes From Baseline (Plaque Assay Analysis) Day 1, 5 hours post-dose	-0.270 log10 pfu/mL Standard Error 0.1607	-2.173 log10 pfu/mL Standard Error 0.2123	-2.189 log10 pfu/mL Standard Error 0.2676	-1.535 log10 pfu/mL Standard Error 0.2526
Viral Load Changes From Baseline (Plaque Assay Analysis) Day 3, 2 hours post-dose	-1.936 log10 pfu/mL Standard Error 0.2317	-2.396 log10 pfu/mL Standard Error 0.2234	-2.134 log10 pfu/mL Standard Error 0.2525	-1.516 log10 pfu/mL Standard Error 0.2558
Viral Load Changes From Baseline (Plaque Assay Analysis) Follow-up	-2.368 log10 pfu/mL Standard Error 0.2946	-2.431 log10 pfu/mL Standard Error 0.2202	-2.279 log10 pfu/mL Standard Error 0.2576	-1.416 log10 pfu/mL Standard Error 0.2821

SECONDARY outcome

Timeframe: From Baseline until Day 14 (Follow-up) (Baseline; Day 1, 5 hours post-dose; Day 3, 2 hours post-dose; and Follow-up reported)

Change from Baseline in RSV Load measured by RT-qPCR (RSV Infected Population)

Outcome measures

Outcome measures
Measure	Placebo n=35 Participants Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg n=40 Participants Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg n=40 Participants Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg n=38 Participants Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Viral Load Changes From Baseline (RT-qPCR Analysis) Baseline	5.236 log10 copies/mL Standard Error 0.2827	4.966 log10 copies/mL Standard Error 0.2095	5.232 log10 copies/mL Standard Error 0.1899	4.525 log10 copies/mL Standard Error 0.2937
Viral Load Changes From Baseline (RT-qPCR Analysis) Day 1, 5 hours post-dose	-0.221 log10 copies/mL Standard Error 0.1601	-0.544 log10 copies/mL Standard Error 0.1286	-0.241 log10 copies/mL Standard Error 0.2031	-0.449 log10 copies/mL Standard Error 0.1883
Viral Load Changes From Baseline (RT-qPCR Analysis) Day 3, 2 hours post-dose	-2.156 log10 copies/mL Standard Error 0.2454	-2.589 log10 copies/mL Standard Error 0.2138	-2.310 log10 copies/mL Standard Error 0.2797	-2.025 log10 copies/mL Standard Error 0.2840
Viral Load Changes From Baseline (RT-qPCR Analysis) Follow-up	-3.413 log10 copies/mL Standard Error 0.3715	-3.665 log10 copies/mL Standard Error 0.2203	-3.972 log10 copies/mL Standard Error 0.2032	-3.033 log10 copies/mL Standard Error 0.3252

SECONDARY outcome

Timeframe: From Baseline until Day 14 (Follow-up) (Baseline, Day 3, and Follow-up reported)

The time-weighted average change from baseline to Day x was defined as (AUCx - x\* viral load at baseline) /x, where AUCx denotes the AUC between baseline and Day x. For subjects who only had data up to Day t (t\<x), the endpoint was defined as (AUCt - t\*viral load at baseline) / t.

Outcome measures

Outcome measures
Measure	Placebo n=35 Participants Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg n=40 Participants Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg n=40 Participants Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg n=38 Participants Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Viral Load Time-weighted Average Changes From Baseline (Plaque Assay Analysis) Baseline	3.494 log10 pfu/mL Standard Error 0.2396	3.312 log10 pfu/mL Standard Error 0.2165	3.135 log10 pfu/mL Standard Error 0.2430	2.385 log10 pfu/mL Standard Error 0.2526
Viral Load Time-weighted Average Changes From Baseline (Plaque Assay Analysis) Day 3	-1.014 log10 pfu/mL Standard Error 0.1540	-1.924 log10 pfu/mL Standard Error 0.1659	-1.804 log10 pfu/mL Standard Error 0.2098	-1.330 log10 pfu/mL Standard Error 0.2434
Viral Load Time-weighted Average Changes From Baseline (Plaque Assay Analysis) Follow-Up	-2.096 log10 pfu/mL Standard Error 0.2443	-2.295 log10 pfu/mL Standard Error 0.2116	-2.028 log10 pfu/mL Standard Error 0.2217	-1.419 log10 pfu/mL Standard Error 0.2488

SECONDARY outcome

Timeframe: From Baseline until Day 14 (Follow-up) (Baseline, Day 3, and Follow-up reported)

Outcome measures

Outcome measures
Measure	Placebo n=35 Participants Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg n=40 Participants Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg n=40 Participants Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg n=38 Participants Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Viral Load Time-weighted Average Changes From Baseline (RT-qPCR Analysis) Baseline	5.236 log10 copies/mL Standard Error 0.2827	4.966 log10 copies/mL Standard Error 0.2095	5.232 log10 copies/mL Standard Error 0.1899	4.525 log10 copies/mL Standard Error 0.2937
Viral Load Time-weighted Average Changes From Baseline (RT-qPCR Analysis) Day 3	-0.933 log10 copies/mL Standard Error 0.1421	-1.209 log10 copies/mL Standard Error 0.1301	-1.113 log10 copies/mL Standard Error 0.1932	-0.842 log10 copies/mL Standard Error 0.1842
Viral Load Time-weighted Average Changes From Baseline (RT-qPCR Analysis) Follow-up	-2.684 log10 copies/mL Standard Error 0.2263	-2.828 log10 copies/mL Standard Error 0.2099	-2.756 log10 copies/mL Standard Error 0.1831	-2.292 log10 copies/mL Standard Error 0.2581

SECONDARY outcome

Timeframe: Overall Study Period (i.e., approximately 28 days)

Population: The Safety Population consisted of all subjects who received at least 1 administration of study drug. When using this population, the subjects were classified as treated (i.e., using the treatment that the subject actually received). Number of subjects with non-missing ADA results were: placebo:39; ALX-0171 3.0mg/kg:45; 6.0mg/kg:44; 9.0mg/kg:46.

The number of subjects with treatment-emergent (TE) anti-drug antibodies (ADA; TE ADA) based on ADA assay by treatment group for the Safety Population. Blood samples for immunogenicity assessments were collected at Baseline and on Day 14. Immunogenicity data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.

Outcome measures

Outcome measures
Measure	Placebo n=39 Participants Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg n=45 Participants Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg n=44 Participants Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg n=46 Participants Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Immunogenicity; Number of Subjects With Treatment-emergent Anti-drug Antibodies Total TE ADA Positive	10 Participants	15 Participants	16 Participants	15 Participants
Immunogenicity; Number of Subjects With Treatment-emergent Anti-drug Antibodies Total TE ADA Negative	16 Participants	17 Participants	14 Participants	13 Participants
Immunogenicity; Number of Subjects With Treatment-emergent Anti-drug Antibodies TE ADA Equivocal	12 Participants	12 Participants	13 Participants	14 Participants
Immunogenicity; Number of Subjects With Treatment-emergent Anti-drug Antibodies TE ADA Inconclusive	1 Participants	1 Participants	1 Participants	4 Participants

SECONDARY outcome

Timeframe: Overall Study Period (i.e., approximately 28 days)

Population: The Safety Population consisted of all subjects who received at least 1 administration of study drug. When using this population, the subjects were classified as treated (i.e., using the treatment that the subject actually received).Number of subjects with non-missing NAb results were: placebo:39; ALX-0171 3.0mg/kg:45; 6.0mg/kg:44; 9.0mg/kg:46.

Number of subjects with treatment-emergent neutralizing antibodies (TE NAb) as detected with the competitive ligand binding NAb assay. Blood samples for immunogenicity assessments were collected at Baseline and on Day 14. Immunogenicity data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.

Outcome measures

Outcome measures
Measure	Placebo n=39 Participants Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg n=45 Participants Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg n=44 Participants Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg n=46 Participants Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Immunogenicity; Number of Subjects With Treatment-emergent Neutralizing Antibodies Post-dose Positive	2 Participants	11 Participants	18 Participants	12 Participants
Immunogenicity; Number of Subjects With Treatment-emergent Neutralizing Antibodies Post-dose Negative	36 Participants	33 Participants	26 Participants	31 Participants
Immunogenicity; Number of Subjects With Treatment-emergent Neutralizing Antibodies Post-dose Missing	1 Participants	1 Participants	0 Participants	3 Participants

Adverse Events

Placebo

Serious events: 5 serious events

Other events: 17 other events

Deaths: 0 deaths

ALX-0171 3.0 mg/kg

Serious events: 4 serious events

Other events: 16 other events

Deaths: 0 deaths

ALX-0171 6.0 mg/kg

Serious events: 3 serious events

Other events: 16 other events

Deaths: 0 deaths

ALX-0171 9.0mg/kg

Serious events: 3 serious events

Other events: 10 other events

Deaths: 0 deaths

Serious adverse events

Serious adverse events
Measure	Placebo n=40 participants at risk Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg n=45 participants at risk Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg n=44 participants at risk Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg n=46 participants at risk Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Respiratory, thoracic and mediastinal disorders Respiratory failure	0.00% 0/40 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/45 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.3% 1/44 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/46 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
General disorders Vessel puncture site phlebitis	0.00% 0/40 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/45 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.3% 1/44 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/46 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Infections and infestations Pneumonia bacterial	2.5% 1/40 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/45 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.3% 1/44 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.2% 1/46 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Infections and infestations Bronchiolitis	2.5% 1/40 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.2% 1/45 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/44 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/46 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Infections and infestations Bronchitis	2.5% 1/40 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.2% 1/45 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/44 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/46 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Infections and infestations Gastroenteritis	0.00% 0/40 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.2% 1/45 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/44 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/46 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Infections and infestations Pneumonococcal bacteraemia	0.00% 0/40 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/45 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/44 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.2% 1/46 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Infections and infestations Pneumonia	0.00% 0/40 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/45 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/44 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.2% 1/46 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Infections and infestations Respiratory syncytial virus infection	0.00% 0/40 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.2% 1/45 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/44 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/46 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Infections and infestations Influenza	2.5% 1/40 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/45 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/44 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/46 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Infections and infestations Pneumonia viral	2.5% 1/40 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/45 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/44 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/46 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.

Other adverse events

Other adverse events
Measure	Placebo n=40 participants at risk Inhalation of Placebo once daily for 3 consecutive days	ALX-0171 3.0 mg/kg n=45 participants at risk Inhalation of ALX-0171 3.0 mg/kg once daily for 3 consecutive days	ALX-0171 6.0 mg/kg n=44 participants at risk Inhalation of ALX-0171 6.0 mg/kg once daily for 3 consecutive days	ALX-0171 9.0mg/kg n=46 participants at risk Inhalation of ALX-0171 9.0 mg/kg once daily for 3 consecutive days
Blood and lymphatic system disorders Anaemia	5.0% 2/40 • Number of events 2 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/45 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.3% 1/44 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/46 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Respiratory, thoracic and mediastinal disorders Rhinorrhea	2.5% 1/40 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	13.3% 6/45 • Number of events 7 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	6.8% 3/44 • Number of events 3 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	4.3% 2/46 • Number of events 2 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Respiratory, thoracic and mediastinal disorders Cough	2.5% 1/40 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	4.4% 2/45 • Number of events 2 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	6.8% 3/44 • Number of events 3 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	4.3% 2/46 • Number of events 2 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
General disorders Pyrexia	2.5% 1/40 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	4.4% 2/45 • Number of events 3 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	9.1% 4/44 • Number of events 4 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/46 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Gastrointestinal disorders Diarrhoea	5.0% 2/40 • Number of events 2 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.2% 1/45 • Number of events 2 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/44 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/46 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Skin and subcutaneous tissue disorders Rash	5.0% 2/40 • Number of events 2 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/45 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/44 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/46 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Infections and infestations Upper respiratory tract infection	7.5% 3/40 • Number of events 3 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	6.7% 3/45 • Number of events 3 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	6.8% 3/44 • Number of events 4 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	4.3% 2/46 • Number of events 2 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Infections and infestations Conjuctivitis	5.0% 2/40 • Number of events 2 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	4.4% 2/45 • Number of events 2 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.3% 1/44 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.2% 1/46 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Infections and infestations Rhinitis	0.00% 0/40 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/45 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	2.3% 1/44 • Number of events 1 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	6.5% 3/46 • Number of events 3 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.
Infections and infestations Otitis media	7.5% 3/40 • Number of events 3 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/45 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/44 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.	0.00% 0/46 • All adverse events (AEs) were reported from first study drug intake to the end of study visit (Day 28) or withdrawal visit. A treatment-emergent AE (TEAE) was defined as any AE starting or worsening in severity (for preexisting conditions) from the start of study drug administration, until completion of the subject's last visit. Adverse event data were analyzed using the Safety Population. This population differs from the ITT and mITT Populations as 2 subjects who were originally randomized to placebo, received active treatment once; one subject received ALX-0171 6.0 mg/kg and one subject ALX-0171 9.0 mg/kg.

Additional Information

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Results disclosure agreements

Principal investigator is a sponsor employee Publication of any results from this study will be according to the principles of the Declaration of Helsinki, and will require prior review and written agreement of the Sponsor.
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