Trial Outcomes & Findings for Study of a Single Intramuscular Dose of Nirsevimab in the Prevention of Hospitalizations Due to Respiratory Syncytial Virus (RSV) Infection in Healthy Term and Preterm Infants During the First Year of Life (NCT NCT05437510)

Last Updated: 2025-10-09

Results Overview

LRTI included the following common symptoms: clinical finding of rhonchi, rales, crackles, or wheeze; increased respiratory rate at rest (age: \<2 months, ≥60 breaths per minute (/min); 2 to 6 months, ≥50 breaths/min; \>6 months, ≥40 breaths/min), and hypoxemia (in room air: oxygen saturation \<95%). Hospitalization was defined as the decision to admit to in-patient care by the treating physician. RSV season was the period of increased RSV infection.

Recruitment status

COMPLETED

Study phase

PHASE3

Target enrollment

8057 participants

Primary outcome timeframe

From dosing/randomization (Day 1) up to approximately 7 months

Results posted on

2025-10-09

Participant Flow

The study was conducted at 235 investigational sites in France, Germany and the United Kingdom (UK).

Total 8057 participants were enrolled and randomized in 1:1 ratio to nirsevimab or no intervention group between 08 August 2022 to 28 February 2023. Participants were followed up for safety for 12-months (366 days) (for France, Germany, and UK non-reconsented participants) and for 24 months (731 days) (for UK participants who consented to take part into study extension \[UK reconsented participants\]). As pre-specified in protocol and SAP, results are presented by treatment group.

Participant milestones

Participant milestones
Measure	Nirsevimab Participants received nirsevimab 50 milligrams (mg) (if weight \<5 kilograms \[kg\]) or 100 mg (if weight ≥5 kg) as a single intramuscular (IM) injection on Day 1.	No Intervention Participants received no respiratory syncytial virus (RSV) preventive intervention on Day 1.
Overall Study STARTED	4038	4019
Overall Study Randomized and Treated	4015	1
Overall Study Participants Entered Study Extension	1142	1084
Overall Study COMPLETED	3747	3631
Overall Study NOT COMPLETED	291	388

Reasons for withdrawal

Reasons for withdrawal
Measure	Nirsevimab Participants received nirsevimab 50 milligrams (mg) (if weight \<5 kilograms \[kg\]) or 100 mg (if weight ≥5 kg) as a single intramuscular (IM) injection on Day 1.	No Intervention Participants received no respiratory syncytial virus (RSV) preventive intervention on Day 1.
Overall Study Adverse Event	2	1
Overall Study Protocol Deviation	1	6
Overall Study Withdrawal by Parent/Guardian	23	23
Overall Study Lost to Follow-up	265	358

Baseline Characteristics

Race and Ethnicity were not collected from any participant.

Baseline characteristics by cohort

Baseline characteristics by cohort
Measure	Nirsevimab n=4038 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.	No Intervention n=4019 Participants Participants received no RSV preventive intervention on Day 1.	Total n=8057 Participants Total of all reporting groups
Age, Continuous	4.53 months STANDARD_DEVIATION 3.342 • n=4038 Participants	4.48 months STANDARD_DEVIATION 3.294 • n=4019 Participants	4.51 months STANDARD_DEVIATION 3.318 • n=8057 Participants
Sex: Female, Male Female	1950 Participants n=4038 Participants	1912 Participants n=4019 Participants	3862 Participants n=8057 Participants
Sex: Female, Male Male	2088 Participants n=4038 Participants	2107 Participants n=4019 Participants	4195 Participants n=8057 Participants
Race and Ethnicity Not Collected	—	—	0 Participants Race and Ethnicity were not collected from any participant.

PRIMARY outcome

Timeframe: From dosing/randomization (Day 1) up to approximately 7 months

Population: The All Randomized Set consisted of all participants randomly assigned to either the nirsevimab group or the no intervention group.

Outcome measures

Outcome measures
Measure	No Intervention n=4019 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=4038 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Respiratory Syncytial Virus (RSV) Lower Respiratory Tract Infection (LRTI) Hospitalization Through the Respiratory Syncytial Virus Season	64 Participants	11 Participants

SECONDARY outcome

Timeframe: From dosing/randomization (Day 1) up to approximately 7 months

Population: The All Randomized Set consisted of all participants randomly assigned to either the nirsevimab group or the no intervention group.

LRTI included the following common symptoms: clinical finding of rhonchi, rales, crackles, or wheeze; increased respiratory rate at rest (age: \<2 months, ≥60 breaths/min; 2 to 6 months, ≥50 breaths/min; \>6 months, ≥40 breaths/min), and hypoxemia (in room air: oxygen saturation \<95%). Very severe RSV LRTI was defined as RSV LRTI hospitalization with oxygen saturation \<90% (at any time during hospitalization) and oxygen supplementation. Hospitalization was defined as the decision to admit to in-patient care by the treating physician. RSV season was the period of increased RSV infection.

Outcome measures

Outcome measures
Measure	No Intervention n=4019 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=4038 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Very Severe Respiratory Syncytial Virus Lower Respiratory Tract Infection Through the Respiratory Syncytial Virus Season	21 Participants	5 Participants

SECONDARY outcome

Timeframe: From dosing/randomization (Day 1) up to approximately 7 months

Population: The All Randomized Set consisted of all participants randomly assigned to either the nirsevimab group or the no intervention group. 'Number Analyzed' indicates the number of participants with data collected for each specified category.

LRTI included the following common symptoms: clinical finding of rhonchi, rales, crackles, or wheeze; increased respiratory rate at rest (age: \<2 months, ≥60 breaths/min; 2 to 6 months, ≥50 breaths/min; \>6 months, ≥40 breaths/min), and hypoxemia (in room air: oxygen saturation \<95%). Hospitalization was defined as the decision to admit to in-patient care by the treating physician. RSV season was the period of increased RSV infection. Number of participants with RSV LRTI hospitalization through the RSV season in France, UK, and Germany is presented.

Outcome measures

Outcome measures
Measure	No Intervention n=4019 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=4038 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization Through the Respiratory Syncytial Virus Season in Each Country Germany	19 Participants	5 Participants
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization Through the Respiratory Syncytial Virus Season in Each Country France	28 Participants	3 Participants
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization Through the Respiratory Syncytial Virus Season in Each Country United Kingdom	17 Participants	3 Participants

SECONDARY outcome

Timeframe: From dosing/randomization (Day 1) up to approximately 7 months

LRTI included the following common symptoms: clinical finding of rhonchi, rales, crackles, or wheeze; increased respiratory rate at rest (age: \<2 months, ≥60 breaths/min; 2 to 6 months, ≥50 breaths/min; \>6 months, ≥40 breaths/min), and hypoxemia (in room air: oxygen saturation \<95%). Hospitalization was defined as the decision to admit to in-patient care by the treating physician. RSV season was the period of increased RSV infection. Number of participants with hospitalization for all-cause LRTI through the RSV season in France, UK, Germany, and overall is presented.

Outcome measures

Outcome measures
Measure	No Intervention n=4019 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=4038 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Hospitalization for All-Cause Lower Respiratory Tract Infection Through the Respiratory Syncytial Virus Season Overall	106 Participants	48 Participants
Number of Participants With Hospitalization for All-Cause Lower Respiratory Tract Infection Through the Respiratory Syncytial Virus Season France	44 Participants	24 Participants
Number of Participants With Hospitalization for All-Cause Lower Respiratory Tract Infection Through the Respiratory Syncytial Virus Season United Kingdom	39 Participants	17 Participants
Number of Participants With Hospitalization for All-Cause Lower Respiratory Tract Infection Through the Respiratory Syncytial Virus Season Germany	23 Participants	7 Participants

SECONDARY outcome

Timeframe: From dosing/randomization (Day 1) to Day 151

LRTI included the following common symptoms: clinical finding of rhonchi, rales, crackles, or wheeze; increased respiratory rate at rest (age: \<2 months, ≥60 breaths/min; 2 to 6 months, ≥50 breaths/min; \>6 months, ≥40 breaths/min), and hypoxemia (in room air: oxygen saturation \<95%). Hospitalization was defined as the decision to admit to in-patient care by the treating physician. Number of participants with RSV LRTI hospitalization through 151 days post-dosing/randomization in France, UK, Germany, and overall is presented.

Outcome measures

Outcome measures
Measure	No Intervention n=4019 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=4038 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization Through 151 Days Post-dosing/Randomization Germany	19 Participants	5 Participants
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization Through 151 Days Post-dosing/Randomization Overall	67 Participants	12 Participants
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization Through 151 Days Post-dosing/Randomization France	28 Participants	4 Participants
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization Through 151 Days Post-dosing/Randomization United Kingdom	20 Participants	3 Participants

SECONDARY outcome

Timeframe: From dosing/randomization (Day 1) to Day 151

LRTI included the following common symptoms: clinical finding of rhonchi, rales, crackles, or wheeze; increased respiratory rate at rest (age: \<2 months, ≥60 breaths/min; 2 to 6 months, ≥50 breaths/min; \>6 months, ≥40 breaths/min), and hypoxemia (in room air: oxygen saturation \<95%). Very severe RSV LRTI was defined as RSV LRTI hospitalization with oxygen saturation \<90% (at any time during hospitalization) and oxygen supplementation. Hospitalization was defined as the decision to admit to in-patient care by the treating physician. Number of participants with very severe RSV LRTI through 151 days post-dosing/randomization in France, UK, Germany, and overall is presented.

Outcome measures

Outcome measures
Measure	No Intervention n=4019 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=4038 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Very Severe Respiratory Syncytial Virus Lower Respiratory Tract Infection Through 151 Days Post-dosing/Randomization Overall	24 Participants	6 Participants
Number of Participants With Very Severe Respiratory Syncytial Virus Lower Respiratory Tract Infection Through 151 Days Post-dosing/Randomization France	9 Participants	2 Participants
Number of Participants With Very Severe Respiratory Syncytial Virus Lower Respiratory Tract Infection Through 151 Days Post-dosing/Randomization United Kingdom	11 Participants	1 Participants
Number of Participants With Very Severe Respiratory Syncytial Virus Lower Respiratory Tract Infection Through 151 Days Post-dosing/Randomization Germany	4 Participants	3 Participants

SECONDARY outcome

Timeframe: From dosing/randomization (Day 1) to Day 151

LRTI included the following common symptoms: clinical finding of rhonchi, rales, crackles, or wheeze; increased respiratory rate at rest (age: \<2 months, ≥60 breaths/min; 2 to 6 months, ≥50 breaths/min; \>6 months, ≥40 breaths/min), and hypoxemia (in room air: oxygen saturation \<95%). Hospitalization was defined as the decision to admit to in-patient care by the treating physician. Number of participants with hospitalization for all-cause LRTI through 151 days post-dosing/randomization in France, UK, Germany, and overall is presented.

Outcome measures

Outcome measures
Measure	No Intervention n=4019 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=4038 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Hospitalization for All-Cause Lower Respiratory Tract Infection Through 151 Days Post-dosing/Randomization Overall	132 Participants	76 Participants
Number of Participants With Hospitalization for All-Cause Lower Respiratory Tract Infection Through 151 Days Post-dosing/Randomization France	48 Participants	32 Participants
Number of Participants With Hospitalization for All-Cause Lower Respiratory Tract Infection Through 151 Days Post-dosing/Randomization United Kingdom	58 Participants	35 Participants
Number of Participants With Hospitalization for All-Cause Lower Respiratory Tract Infection Through 151 Days Post-dosing/Randomization Germany	26 Participants	9 Participants

SECONDARY outcome

Timeframe: Up to 30 minutes post-dosing/randomization on Day 1

Population: The Safety Analysis Set (SafAS) consisted of all participants who received nirsevimab in the study and all randomized participants who were randomized to the no intervention group and did not receive nirsevimab inadvertently. As pre-specified in the protocol and SAP, results are presented by treatment group.

An adverse event (AE) was any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. TEAEs were either events with the start date and time posterior to the start of the treatment period and up to the end of the treatment period or events with the start date and time prior to the start of the treatment period, whose severity was greater than 1 or missing and stop date is missing or not before the treatment period. Immediate events were recorded to capture medically relevant AEs which occurred within the first 30 minutes after immunization.

Outcome measures

Outcome measures
Measure	No Intervention n=4018 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=4016 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Immediate Treatment-Emergent Adverse Events (TEAEs)	0 Participants	27 Participants

SECONDARY outcome

Timeframe: From dosing/randomization (Day 1) to Day 31

Population: The SafAS consisted of all participants who received nirsevimab in the study and all randomized participants who were randomized to the no intervention group and did not receive nirsevimab inadvertently. As pre-specified in the protocol and SAP, results are presented by treatment group.

Outcome measures

Outcome measures
Measure	No Intervention n=4018 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=4016 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Non-Serious Treatment-Emergent Adverse Events	1265 Participants	1316 Participants

SECONDARY outcome

Timeframe: From dosing/randomization (Day 1) to Day 366

AE: untoward medical occurrence in clinical study participant, temporally associated with use of study intervention, whether or not related to it. TEAEs: events with start date/time posterior to start of treatment period(TP) and up to end of TP, or events with start date/time prior to start of TP, whose severity was\>1/missing; stop date was missing/not before TP. SAE: AE at any dose resulting in death, persistent or significant disability/incapacity, required inpatient hospitalization/prolongation of existing hospitalization, was life-threatening or congenital anomaly/birth defect or medically important event. MAAE: new onset/worsening of condition that prompted participant or participant's parent/legally acceptable representative to seek unplanned medical advice at physician's office/Emergency Department. AESI: scientific, medical concern specific to Sponsor's study intervention/program for which ongoing monitoring and rapid communication by investigator to Sponsor was appropriate.

Outcome measures

Outcome measures
Measure	No Intervention n=4018 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=4016 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Treatment-Emergent Serious Adverse Events (SAEs), Treatment-Emergent Adverse Events of Special Interest (AESIs) and Treatment-Emergent Medically Attended Adverse Events (MAAEs) Treatment-emergent SAEs	222 Participants	262 Participants
Number of Participants With Treatment-Emergent Serious Adverse Events (SAEs), Treatment-Emergent Adverse Events of Special Interest (AESIs) and Treatment-Emergent Medically Attended Adverse Events (MAAEs) Treatment-emergent AESIs	3 Participants	11 Participants
Number of Participants With Treatment-Emergent Serious Adverse Events (SAEs), Treatment-Emergent Adverse Events of Special Interest (AESIs) and Treatment-Emergent Medically Attended Adverse Events (MAAEs) Treatment-emergent MAAEs	3100 Participants	3106 Participants

SECONDARY outcome

Timeframe: From Day 366 to Day 731

An AE was any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. TEAEs were either events with the start date and time posterior to the start of the treatment period and up to the end of the treatment period or events with the start date and time prior to the start of the treatment period, whose severity was greater than 1 or missing and stop date is missing or not before the treatment period. SAE: AE at any dose resulting in death, persistent or significant disability/incapacity, required inpatient hospitalization/prolongation of existing hospitalization, was life-threatening or congenital anomaly/birth defect or medically important event. A treatment-related TEAE was a TEAE considered by the investigator as related or with unknown/missing relationship to treatment for participants who received nirsevimab on Day 1.

Outcome measures

Outcome measures
Measure	No Intervention n=1084 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=1140 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Treatment-Related Serious Adverse Event (for United Kingdom Reconsented Participants)	0 Participants	0 Participants

SECONDARY outcome

Timeframe: From dosing/randomization (Day 1) to Day 181

LRTI included the following common symptoms: clinical finding of rhonchi, rales, crackles, or wheeze; increased respiratory rate at rest (age: \<2 months, ≥60 breaths/min; 2 to 6 months, ≥50 breaths/min; \>6 months, ≥40 breaths/min), and hypoxemia (in room air: oxygen saturation \<95%). Hospitalization was defined as the decision to admit to in-patient care by the treating physician. Number of participants with RSV LRTI hospitalization through 181 days post-dosing/randomization in France, UK, Germany, and overall is presented.

Outcome measures

Outcome measures
Measure	No Intervention n=4019 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=4038 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization Through 181 Days Post-dosing/Randomization Overall	68 Participants	12 Participants
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization Through 181 Days Post-dosing/Randomization France	28 Participants	4 Participants
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization Through 181 Days Post-dosing/Randomization United Kingdom	21 Participants	3 Participants
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization Through 181 Days Post-dosing/Randomization Germany	19 Participants	5 Participants

SECONDARY outcome

Timeframe: From dosing/randomization (Day 1) to Day 181

LRTI included the following common symptoms: clinical finding of rhonchi, rales, crackles, or wheeze; increased respiratory rate at rest (age: \<2 months, ≥60 breaths/min; 2 to 6 months, ≥50 breaths/min; \>6 months, ≥40 breaths/min), and hypoxemia (in room air: oxygen saturation \<95%). Hospitalization was defined as the decision to admit to in-patient care by the treating physician. Number of participants with hospitalization for all-cause LRTI through 181 days post-dosing/randomization in France, UK, Germany, and overall is presented.

Outcome measures

Outcome measures
Measure	No Intervention n=4019 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=4038 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Hospitalization for All-Cause Lower Respiratory Tract Infection Through 181 Days Post-dosing/Randomization Overall	138 Participants	82 Participants
Number of Participants With Hospitalization for All-Cause Lower Respiratory Tract Infection Through 181 Days Post-dosing/Randomization France	49 Participants	34 Participants
Number of Participants With Hospitalization for All-Cause Lower Respiratory Tract Infection Through 181 Days Post-dosing/Randomization United Kingdom	62 Participants	38 Participants
Number of Participants With Hospitalization for All-Cause Lower Respiratory Tract Infection Through 181 Days Post-dosing/Randomization Germany	27 Participants	10 Participants

SECONDARY outcome

Timeframe: From Day 181 to Day 366

Population: The All Randomized Set consisted of all participants randomly assigned to either the nirsevimab group or the no intervention group. Only participants with data collected are reported. 'Number Analyzed' indicates the number of participants with data collected for each specified category.

LRTI included the following common symptoms: clinical finding of rhonchi, rales, crackles, or wheeze; increased respiratory rate at rest (age: \<2 months, ≥60 breaths/min; 2 to 6 months, ≥50 breaths/min; \>6 months, ≥40 breaths/min), and hypoxemia (in room air: oxygen saturation \<95%). Hospitalization was defined as the decision to admit to in-patient care by the treating physician. Number of participants with RSV LRTI hospitalization from Days 181 to 366 post-dosing/randomization (with no RSV LRTI hospitalizations before Day 181) in France, UK, Germany, and overall is presented.

Outcome measures

Outcome measures
Measure	No Intervention n=3951 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=4026 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization From Days 181 to 366 Post-dosing/Randomization Overall	28 Participants	31 Participants
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization From Days 181 to 366 Post-dosing/Randomization France	5 Participants	6 Participants
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization From Days 181 to 366 Post-dosing/Randomization United Kingdom	19 Participants	20 Participants
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization From Days 181 to 366 Post-dosing/Randomization Germany	4 Participants	5 Participants

SECONDARY outcome

Timeframe: From Day 181 to Day 366

Population: The All Randomized Set consisted of all participants randomly assigned to either the nirsevimab group or the no intervention group. Only participants with data collected are reported.

LRTI included the following common symptoms: clinical finding of rhonchi, rales, crackles, or wheeze; increased respiratory rate at rest (age: \<2 months, ≥60 breaths/min; 2 to 6 months, ≥50 breaths/min; \>6 months, ≥40 breaths/min), and hypoxemia (in room air: oxygen saturation \<95%). Hospitalization was defined as the decision to admit to in-patient care by the treating physician. Number of participants with hospitalization for all-cause LRTI from Days 181 to 366 post-dosing/randomization (with no hospitalizations for all-cause LRTI before Day 181) is presented.

Outcome measures

Outcome measures
Measure	No Intervention n=3881 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=3956 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Hospitalization for All-Cause Lower Respiratory Tract Infection From Days 181 to 366 Post-dosing/Randomization	55 Participants	68 Participants

SECONDARY outcome

Timeframe: From Day 366 to Day 731

Population: The All Randomized Set consisted of all participants randomly assigned to either the nirsevimab group or the no intervention group. Only participants with data collected are reported.

LRTI included the following common symptoms: clinical finding of rhonchi, rales, crackles, or wheeze; increased respiratory rate at rest (age: \<2 months, ≥60 breaths/min; 2 to 6 months, ≥50 breaths/min; \>6 months, ≥40 breaths/min), and hypoxemia (in room air: oxygen saturation \<95%). Hospitalization was defined as the decision to admit to in-patient care by the treating physician. Number of participants with RSV LRTI hospitalization from Days 366 to 731 post-dosing/randomization (with no RSV LRTI hospitalizations before Day 366) in UK reconsented participants is presented.

Outcome measures

Outcome measures
Measure	No Intervention n=1062 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=1132 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Respiratory Syncytial Virus Lower Respiratory Tract Infection Hospitalization From Days 366 to 731 Post-dosing/Randomization (for United Kingdom Reconsented Participants)	2 Participants	7 Participants

SECONDARY outcome

Timeframe: From Day 366 to Day 731

Population: The All Randomized Set consisted of all participants randomly assigned to either the nirsevimab group or the no intervention group. Only participants with data collected are reported.

LRTI included the following common symptoms: clinical finding of rhonchi, rales, crackles, or wheeze; increased respiratory rate at rest (age: \<2 months, ≥60 breaths/min; 2 to 6 months, ≥50 breaths/min; \>6 months, ≥40 breaths/min), and hypoxemia (in room air: oxygen saturation \<95%). Hospitalization was defined as the decision to admit to in-patient care by the treating physician. Number of participants with hospitalization for all-cause LRTI from Days 366 to 731 post-dosing/randomization (with no hospitalizations for all-cause LRTI before Day 366) in UK reconsented participants is presented.

Outcome measures

Outcome measures
Measure	No Intervention n=1025 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=1096 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Hospitalization for All-Cause Lower Respiratory Tract Infection From Days 366 to 731 Post-dosing/Randomization (for United Kingdom Reconsented Participants)	10 Participants	18 Participants

SECONDARY outcome

Timeframe: From dosing/randomization (Day 1) to Day 731

Population: The All Randomized Set consisted of all participants randomly assigned to either the nirsevimab group or the no intervention group. Only participants with data collected are reported.

Wheeze was defined as a physician-diagnosed wheeze or asthma or related ear, nose and throat (ENT)/respiratory symptoms at an office visit or an illness for which the child was prescribed medication to treat an ENT/respiratory condition. Recurrent wheeze event was defined as 2 or more protocol-defined wheeze episodes throughout follow-up period.

Outcome measures

Outcome measures
Measure	No Intervention n=888 Participants Participants received no RSV preventive intervention on Day 1.	Nirsevimab n=928 Participants Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.
Number of Participants With Recurrent Wheeze (for United Kingdom Reconsented Participants)	96 Participants	101 Participants

Adverse Events

Nirsevimab

Serious events: 262 serious events

Other events: 324 other events

Deaths: 1 deaths

No Intervention

Serious events: 222 serious events

Other events: 279 other events

Deaths: 0 deaths

Serious adverse events

Other adverse events

Other adverse events
Measure	Nirsevimab n=4016 participants at risk Participants received nirsevimab 50 mg (if weight \<5 kg) or 100 mg (if weight ≥5 kg) as a single IM injection on Day 1.	No Intervention n=4018 participants at risk Participants received no RSV preventive intervention on Day 1.
Infections and infestations Nasopharyngitis	8.1% 324/4016 • Number of events 345 • SAEs and all-cause mortality were collected from dosing/randomization (Day 1) up to end of follow-up (Day 366 for France, Germany, UK non-reconsented participants and Day 731 for UK reconsented participants). Non-serious AEs were collected from dosing/randomization (Day 1) up to Day 31 as pre-specified in protocol. Analysis was performed on the SafAS. As pre-specified in the protocol and SAP, results are presented by treatment group. Safety analysis was not planned exclusively for UK reconsented participants, and no separate safety data was collected for this subgroup.	6.9% 279/4018 • Number of events 298 • SAEs and all-cause mortality were collected from dosing/randomization (Day 1) up to end of follow-up (Day 366 for France, Germany, UK non-reconsented participants and Day 731 for UK reconsented participants). Non-serious AEs were collected from dosing/randomization (Day 1) up to Day 31 as pre-specified in protocol. Analysis was performed on the SafAS. As pre-specified in the protocol and SAP, results are presented by treatment group. Safety analysis was not planned exclusively for UK reconsented participants, and no separate safety data was collected for this subgroup.

Additional Information

Trial Transparency Team

Sanofi Pasteur

Phone: 800-633-1610

Email: [email protected]

Results disclosure agreements

Principal investigator is a sponsor employee The Sponsor must have the opportunity to review at least 60 days prior to submission for publication or presentation. If review indicates that potentially patentable subject matter would be disclosed, publication or public disclosure may be delayed for a maximum of an additional 60 days to allow for filing the necessary patent applications.
Publication restrictions are in place

Restriction type: OTHER