Trial Outcomes & Findings for H1N1v Virus Challenge Study in Healthy Subjects (NCT NCT04044352)

Results Overview

Blood samples were collected pre-challenge (Day -2) for the HAI assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. The geometric mean of each sample's replicate results was calculated from available results, then grouped by seroprotection status (titer results \>= 1:40 vs \< 1:40). MMID is a composite endpoint determined by the presence of viral shedding (detected by any approved positive RT-PCR test from a NP swab), accompanied by at least one the following symptoms occurring any time from Day 2 through Day 8; body aches or pain, chest tightness, chills, conjunctivitis, nasal congestion, sinus congestion, coryza, decreased appetite, diarrhea, dry cough, dyspnea, fatigue, fever, headache, lymphopenia, nausea, a 3% or more decrease in oxygen saturation from baseline, productive cough, rhinorrhea, sore throat, and sweats. The percentage of participants that developed MMID was calculated within each pre-challenge seroprotection status group.

Recruitment status

COMPLETED

Study phase

PHASE1

Target enrollment

76 participants

Primary outcome timeframe

Day 2 through Day 8

Results posted on

2021-04-28

Participant Flow

Healthy adults, male and female, between the ages of 18 and 49, who are non-habitual smokers without medical conditions at high risk for severe complications of influenza virus infection were enrolled. Participants were enrolled between 22OCT2019 and 05DEC2019.

Participant milestones

Participant milestones
Measure	Study Group Participants will receive 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
Overall Study STARTED	76
Overall Study COMPLETED	65
Overall Study NOT COMPLETED	11

Reasons for withdrawal

Reasons for withdrawal
Measure	Study Group Participants will receive 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
Overall Study Lost to Follow-up	9
Overall Study Withdrawal by Subject	2

Baseline Characteristics

H1N1v Virus Challenge Study in Healthy Subjects

Baseline characteristics by cohort

Baseline characteristics by cohort
Measure	Study Group n=76 Participants Participants will receive 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1challenge virus administered intranasally via a sprayer on Day 1.
Age, Categorical <=18 years	0 Participants n=5 Participants
Age, Categorical Between 18 and 65 years	76 Participants n=5 Participants
Age, Categorical >=65 years	0 Participants n=5 Participants
Age, Continuous	33.4 years STANDARD_DEVIATION 9.2 • n=5 Participants
Sex: Female, Male Female	30 Participants n=5 Participants
Sex: Female, Male Male	46 Participants n=5 Participants
Ethnicity (NIH/OMB) Hispanic or Latino	5 Participants n=5 Participants
Ethnicity (NIH/OMB) Not Hispanic or Latino	71 Participants n=5 Participants
Ethnicity (NIH/OMB) Unknown or Not Reported	0 Participants n=5 Participants
Race (NIH/OMB) American Indian or Alaska Native	1 Participants n=5 Participants
Race (NIH/OMB) Asian	1 Participants n=5 Participants
Race (NIH/OMB) Native Hawaiian or Other Pacific Islander	0 Participants n=5 Participants
Race (NIH/OMB) Black or African American	35 Participants n=5 Participants
Race (NIH/OMB) White	34 Participants n=5 Participants
Race (NIH/OMB) More than one race	3 Participants n=5 Participants
Race (NIH/OMB) Unknown or Not Reported	2 Participants n=5 Participants
Region of Enrollment United States	76 Participants n=5 Participants
Region of Enrollment United States · Saint Louis University	17 Participants n=5 Participants
Region of Enrollment United States · Cincinnati Children's Hospital	24 Participants n=5 Participants
Region of Enrollment United States · University of Maryland	20 Participants n=5 Participants
Region of Enrollment United States · Duke University	15 Participants n=5 Participants
Receipt of Prior Seasonal Influenza Vaccination (2018-2019) Yes	9 Participants n=5 Participants
Receipt of Prior Seasonal Influenza Vaccination (2018-2019) No	67 Participants n=5 Participants
Receipt of Prior Non-Seasonal Influenza Vaccination (2018-2019) Yes	3 Participants n=5 Participants
Receipt of Prior Non-Seasonal Influenza Vaccination (2018-2019) No	73 Participants n=5 Participants
Baseline Seroprotection (Hemagglutination Inhibition) Low < 1:40	39 Participants n=5 Participants
Baseline Seroprotection (Hemagglutination Inhibition) High >= 1:40	37 Participants n=5 Participants
Baseline Seroprotection (Microneutralization) Low < 1:40	23 Participants n=5 Participants
Baseline Seroprotection (Microneutralization) High >= 1:40	53 Participants n=5 Participants

PRIMARY outcome

Timeframe: Day 2 through Day 8

Population: All participants who received the study challenge, had a baseline sample for immunogenicity, and were followed for the entire duration of the study challenge period, or at least until MMID was observed.

Blood samples were collected pre-challenge (Day -2) for the HAI assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. The geometric mean of each sample's replicate results was calculated from available results, then grouped by seroprotection status (titer results \>= 1:40 vs \< 1:40). MMID is a composite endpoint determined by the presence of viral shedding (detected by any approved positive RT-PCR test from a NP swab), accompanied by at least one the following symptoms occurring any time from Day 2 through Day 8; body aches or pain, chest tightness, chills, conjunctivitis, nasal congestion, sinus congestion, coryza, decreased appetite, diarrhea, dry cough, dyspnea, fatigue, fever, headache, lymphopenia, nausea, a 3% or more decrease in oxygen saturation from baseline, productive cough, rhinorrhea, sore throat, and sweats. The percentage of participants that developed MMID was calculated within each pre-challenge seroprotection status group.

Outcome measures

Outcome measures
Measure	Study Group n=76 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
Percentage of Healthy Participants Reporting Mild-to-Moderate Influenza Disease (MMID) by Baseline A/Bethesda/MM2/H1N1 Hemagglutination Inhibition (HAI) Antibody Seroprotection Status (Titer >/= 1:40 vs. Titer < 1:40) Baseline Seroprotection Status Low < 1:40 : MMID	77 percentage of participants
Percentage of Healthy Participants Reporting Mild-to-Moderate Influenza Disease (MMID) by Baseline A/Bethesda/MM2/H1N1 Hemagglutination Inhibition (HAI) Antibody Seroprotection Status (Titer >/= 1:40 vs. Titer < 1:40) Baseline Seroprotection Status Low < 1:40 : No MMID	23 percentage of participants
Percentage of Healthy Participants Reporting Mild-to-Moderate Influenza Disease (MMID) by Baseline A/Bethesda/MM2/H1N1 Hemagglutination Inhibition (HAI) Antibody Seroprotection Status (Titer >/= 1:40 vs. Titer < 1:40) Baseline Seroprotection Status High > = 1:40 : MMID	65 percentage of participants
Percentage of Healthy Participants Reporting Mild-to-Moderate Influenza Disease (MMID) by Baseline A/Bethesda/MM2/H1N1 Hemagglutination Inhibition (HAI) Antibody Seroprotection Status (Titer >/= 1:40 vs. Titer < 1:40) Baseline Seroprotection Status High > = 1:40 : No MMID	35 percentage of participants

PRIMARY outcome

Timeframe: Day 2 to Day 8

Population: All participants who received the study challenge, had a baseline sample for immunogenicity, and were followed for the entire duration of the study challenge period, or at least until MMID was observed.

Blood samples were collected pre-challenge (Day -2) for the HAI assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. The geometric mean of each sample's replicate results was calculated from available results. MMID is a composite endpoint determined by the presence of viral shedding (detected by any approved positive RT-PCR test from a NP swab), accompanied by at least one the following symptoms occurring any time from Day 2 through Day 8; body aches or pain, chest tightness, chills, conjunctivitis, nasal congestion, sinus congestion, coryza, decreased appetite, diarrhea, dry cough, dyspnea, fatigue, fever, headache, lymphopenia, nausea, a 3% or more decrease in oxygen saturation from baseline, productive cough, rhinorrhea, sore throat, and sweats. The relationship between the level of pre-challenge HAI titer and the likelihood of developing MMID during the study challenge period (Day 2 to Day 8) was assessed via logistic regression.

Outcome measures

Outcome measures
Measure	Study Group n=76 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
Association Between Clinical or Laboratory Manifestation of MMID and A/Bethesda/MM2/H1N1 HAI Antibodies in Serum at Baseline	0.81 Odds Ratio

SECONDARY outcome

Timeframe: Day -2

Population: All participants who received the study challenge, had an available immunogenicity sample for the given study day, and were followed for the entire duration of the study challenge period, or at least until MMID was observed.

Blood samples were collected pre-challenge (Day -2) and post-challenge on Days 8, 29 and 61 for the HAI assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. The geometric mean of each sample's replicate results was calculated from available results. The geometric mean across samples was calculated within each study day and by infection status as observed over the study challenge period (Day 2 to Day 8); RT-PCR Negative (never positive), RT-PCR Positive Asymptomatic (participants with at least one positive PCR result but no symptoms reported), at least once RT-PCR Positive Symptomatic (or MMID).

Outcome measures

Outcome measures
Measure	Study Group n=76 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
Geometric Mean Titer (GMT) of HAI Antibody in Serum at Baseline by Infection Status RT-PCR Positive Symptomatic	36.8 titer Interval 26.1 to 52.0
Geometric Mean Titer (GMT) of HAI Antibody in Serum at Baseline by Infection Status RT-PCR Positive Asymptomatic	20.0 titer Interval 6.9 to 58.0
Geometric Mean Titer (GMT) of HAI Antibody in Serum at Baseline by Infection Status RT-PCR Negative	117.9 titer Interval 61.3 to 227.0

SECONDARY outcome

Timeframe: Day 8

Population: All participants who received the study challenge, had an available immunogenicity sample for the given study day, and were followed for the entire duration of the study challenge period, or at least until MMID was observed.

Blood samples were collected pre-challenge (Day -2) and post-challenge on Days 8, 29 and 61 for the HAI assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. The geometric mean of each sample's replicate results was calculated from available results. The geometric mean across samples was calculated within each study day and by infection status as observed over the study challenge period (Day 2 to Day 8); RT-PCR Negative (never positive), RT-PCR Positive Asymptomatic (participants with at least one positive PCR result but no symptoms reported), at least once RT-PCR Positive Symptomatic (or MMID).

Outcome measures

Outcome measures
Measure	Study Group n=75 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
GMT of HAI Antibody in Serum at Day 8 by Infection Status RT-PCR Positive Symptomatic	46.1 titer Interval 33.2 to 64.0
GMT of HAI Antibody in Serum at Day 8 by Infection Status RT-PCR Positive Asymptomatic	23.7 titer Interval 8.9 to 63.1
GMT of HAI Antibody in Serum at Day 8 by Infection Status RT-PCR Negative	122.5 titer Interval 66.9 to 224.6

SECONDARY outcome

Timeframe: Day 29

Population: All participants who received the study challenge, had an available immunogenicity sample for the given study day, and were followed for the entire duration of the study challenge period, or at least until MMID was observed.

Blood samples were collected pre-challenge (Day -2) and post-challenge on Days 8, 29 and 61 for the HAI assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. The geometric mean of each sample's replicate results was calculated from available results. The geometric mean across samples was calculated within each study day and by infection status as observed over the study challenge period (Day 2 to Day 8); RT-PCR Negative (never positive), RT-PCR Positive Asymptomatic (participants with at least one positive PCR result but no symptoms reported), at least once RT-PCR Positive Symptomatic (or MMID).

Outcome measures

Outcome measures
Measure	Study Group n=67 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
GMT of HAI Antibody in Serum at Day 29 by Infection Status RT-PCR Positive Symptomatic	87.4 titer Interval 65.7 to 116.2
GMT of HAI Antibody in Serum at Day 29 by Infection Status RT-PCR Positive Asymptomatic	63.9 titer Interval 29.2 to 139.9
GMT of HAI Antibody in Serum at Day 29 by Infection Status RT-PCR Negative	126.6 titer Interval 72.3 to 221.9

SECONDARY outcome

Timeframe: Day 61

Population: All participants who received the study challenge, had an available immunogenicity sample for the given study day, and were followed for the entire duration of the study challenge period, or at least until MMID was observed

Blood samples were collected pre-challenge (Day -2) and post-challenge on Days 8, 29 and 61 for the HAI assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. The geometric mean of each sample's replicate results was calculated from available results. The geometric mean across samples was calculated within each study day and by infection status as observed over the study challenge period (Day 2 to Day 8); RT-PCR Negative (never positive), RT-PCR Positive Asymptomatic (participants with at least one positive PCR result but no symptoms reported), at least once RT-PCR Positive Symptomatic (or MMID).

Outcome measures

Outcome measures
Measure	Study Group n=62 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
GMT of HAI Antibody in Serum at Day 61 by Infection Status RT-PCR Positive Symptomatic	78.0 titer Interval 55.5 to 109.7
GMT of HAI Antibody in Serum at Day 61 by Infection Status RT-PCR Positive Asymptomatic	71.3 titer Interval 33.6 to 151.1
GMT of HAI Antibody in Serum at Day 61 by Infection Status RT-PCR Negative	123.1 titer Interval 63.9 to 237.3

SECONDARY outcome

Timeframe: Day 8

Population: All participants who received the study challenge, had an available immunogenicity sample for the given study day, and were followed for the entire duration of the study challenge period, or at least until MMID was observed

Blood samples were collected pre-challenge (Day -2) and post-challenge on Days 8, 29 and 61 for the HAI assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. Seroconversion was defined as a pre-challenge titer 1:10 or greater and a minimum 4-fold rise in post-challenge antibody titer. The percentage of participants achieving seroconversion was calculated within each post-challenge study day and by infection status as observed over the study challenge period (Day 2 to Day 8); RT-PCR Negative (never positive), RT-PCR Positive Asymptomatic (participants with at least one positive PCR result but no symptoms reported), at least once RT-PCR Positive Symptomatic (or MMID).

Outcome measures

Outcome measures
Measure	Study Group n=75 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
Percentage of Healthy Participants Achieving HAI Seroconversion From Baseline in Serum at Day 8 by Infection Status RT-PCR Positive Symptomatic	3.8 percentage of participants Interval 0.5 to 13.0
Percentage of Healthy Participants Achieving HAI Seroconversion From Baseline in Serum at Day 8 by Infection Status RT-PCR Positive Asymptomatic	0 percentage of participants Interval 0.0 to 36.9
Percentage of Healthy Participants Achieving HAI Seroconversion From Baseline in Serum at Day 8 by Infection Status RT-PCR Negative	0 percentage of participants Interval 0.0 to 23.2

SECONDARY outcome

Timeframe: Day 29

Population: All participants who received the study challenge, had an available immunogenicity sample for the given study day, and were followed for the entire duration of the study challenge period, or at least until MMID was observed

Blood samples were collected pre-challenge (Day -2) and post-challenge on Days 8, 29 and 61 for the HAI assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. Seroconversion was defined as a pre-challenge titer 1:10 or greater and a minimum 4-fold rise in post-challenge antibody titer. The percentage of participants achieving seroconversion was calculated within each post-challenge study day and by infection status as observed over the study challenge period (Day 2 to Day 8); RT-PCR Negative (never positive), RT-PCR Positive Asymptomatic (participants with at least one positive PCR result but no symptoms reported), at least once RT-PCR Positive Symptomatic (or MMID).

Outcome measures

Outcome measures
Measure	Study Group n=67 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
Percentage of Healthy Participants Achieving HAI Seroconversion in Serum From Baseline at Day 29 by Infection Status RT-PCR Positive Symptomatic	28.3 percentage of participants Interval 16.0 to 43.5
Percentage of Healthy Participants Achieving HAI Seroconversion in Serum From Baseline at Day 29 by Infection Status RT-PCR Positive Asymptomatic	28.6 percentage of participants Interval 3.7 to 71.0
Percentage of Healthy Participants Achieving HAI Seroconversion in Serum From Baseline at Day 29 by Infection Status RT-PCR Negative	0 percentage of participants Interval 0.0 to 23.2

SECONDARY outcome

Timeframe: Day 61

Population: All participants who received the study challenge, had an available immunogenicity sample for the given study day, and were followed for the entire duration of the study challenge period, or at least until MMID was observed

Blood samples were collected pre-challenge (Day -2) and post-challenge on Days 8, 29 and 61 for the HAI assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. Seroconversion was defined as a pre-challenge titer 1:10 or greater and a minimum 4-fold rise in post-challenge antibody titer. The percentage of participants achieving seroconversion was calculated within each post-challenge study day and by infection status as observed over the study challenge period (Day 2 to Day 8); RT-PCR Negative (never positive), RT-PCR Positive Asymptomatic (participants with at least one positive PCR result but no symptoms reported), at least once RT-PCR Positive Symptomatic (or MMID).

Outcome measures

Outcome measures
Measure	Study Group n=62 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
Percentage of Healthy Participants Achieving HAI Seroconversion in Serum From Baseline at Day 61 by Infection Status RT-PCR Positive Symptomatic	18.6 percentage of participants Interval 8.4 to 33.4
Percentage of Healthy Participants Achieving HAI Seroconversion in Serum From Baseline at Day 61 by Infection Status RT-PCR Positive Asymptomatic	33.3 percentage of participants Interval 4.3 to 77.7
Percentage of Healthy Participants Achieving HAI Seroconversion in Serum From Baseline at Day 61 by Infection Status RT-PCR Negative	0 percentage of participants Interval 0.0 to 24.7

SECONDARY outcome

Timeframe: Day -2

Population: All participants who received the study challenge, had an available immunogenicity sample for the given study day, and were followed for the entire duration of the study challenge period, or at least until MMID was observed

Blood samples were collected pre-challenge (Day -2) and post-challenge on Days 8, 29 and 61 for the MN assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. The geometric mean of each sample's replicate results was calculated from available results. The geometric mean across samples was calculated within each study day and by infection status as observed over the study challenge period (Day 2 to Day 8); RT-PCR Negative (never positive), RT-PCR Positive Asymptomatic (participants with at least one positive PCR result but no symptoms reported), at least once RT-PCR Positive Symptomatic (or MMID).

Outcome measures

Outcome measures
Measure	Study Group n=76 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
GMT of Microneutralization (MN) Antibody in Serum at Baseline by Infection Status RT-PCR Negative	276.7 titer Interval 124.8 to 613.1
GMT of Microneutralization (MN) Antibody in Serum at Baseline by Infection Status RT-PCR Positive Symptomatic	62.9 titer Interval 43.1 to 91.9
GMT of Microneutralization (MN) Antibody in Serum at Baseline by Infection Status RT-PCR Positive Asymptomatic	44.3 titer Interval 13.8 to 142.6

SECONDARY outcome

Timeframe: Day 8

Population: All participants who received the study challenge, had an available immunogenicity sample for the given study day, and were followed for the entire duration of the study challenge period, or at least until MMID was observed

Blood samples were collected pre-challenge (Day -2) and post-challenge on Days 8, 29 and 61 for the MN assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. The geometric mean of each sample's replicate results was calculated from available results. The geometric mean across samples was calculated within each study day and by infection status as observed over the study challenge period (Day 2 to Day 8); RT-PCR Negative (never positive), RT-PCR Positive Asymptomatic (participants with at least one positive PCR result but no symptoms reported), at least once RT-PCR Positive Symptomatic (or MMID).

Outcome measures

Outcome measures
Measure	Study Group n=75 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
GMT of MN Antibody in Serum at Day 8 by Infection Status RT-PCR Positive Symptomatic	87.7 titer Interval 61.7 to 124.6
GMT of MN Antibody in Serum at Day 8 by Infection Status RT-PCR Positive Asymptomatic	52.4 titer Interval 16.6 to 165.5
GMT of MN Antibody in Serum at Day 8 by Infection Status RT-PCR Negative	250.6 titer Interval 112.8 to 556.9

SECONDARY outcome

Timeframe: Day 29

Population: All participants who received the study challenge, had an available immunogenicity sample for the given study day, and were followed for the entire duration of the study challenge period, or at least until MMID was observed

Blood samples were collected pre-challenge (Day -2) and post-challenge on Days 8, 29 and 61 for the MN assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. The geometric mean of each sample's replicate results was calculated from available results. The geometric mean across samples was calculated within each study day and by infection status as observed over the study challenge period (Day 2 to Day 8); RT-PCR Negative (never positive), RT-PCR Positive Asymptomatic (participants with at least one positive PCR result but no symptoms reported), at least once RT-PCR Positive Symptomatic (or MMID).

Outcome measures

Outcome measures
Measure	Study Group n=67 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
GMT of MN Antibody in Serum at Day 29 by Infection Status RT-PCR Positive Symptomatic	159.5 titer Interval 115.7 to 220.1
GMT of MN Antibody in Serum at Day 29 by Infection Status RT-PCR Positive Asymptomatic	103.1 titer Interval 41.5 to 255.9
GMT of MN Antibody in Serum at Day 29 by Infection Status RT-PCR Negative	320.0 titer Interval 157.9 to 648.5

SECONDARY outcome

Timeframe: Day 61

Population: All participants who received the study challenge, had an available immunogenicity sample for the given study day, and were followed for the entire duration of the study challenge period, or at least until MMID was observed

Blood samples were collected pre-challenge (Day -2) and post-challenge on Days 8, 29 and 61 for the MN assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. The geometric mean of each sample's replicate results was calculated from available results. The geometric mean across samples was calculated within each study day and by infection status as observed over the study challenge period (Day 2 to Day 8); RT-PCR Negative (never positive), RT-PCR Positive Asymptomatic (participants with at least one positive PCR result but no symptoms reported), at least once RT-PCR Positive Symptomatic (or MMID).

Outcome measures

Outcome measures
Measure	Study Group n=62 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
GMT of MN Antibody in Serum at Day 61 by Infection Status RT-PCR Positive Symptomatic (MMID-1)	151.8 titer Interval 108.7 to 211.9
GMT of MN Antibody in Serum at Day 61 by Infection Status RT-PCR Positive Asymptomatic	107.2 titer Interval 30.4 to 377.8
GMT of MN Antibody in Serum at Day 61 by Infection Status RT-PCR Negative	287.6 titer Interval 134.9 to 613.2

SECONDARY outcome

Timeframe: Day 8

Population: All participants who received the study challenge, had an available immunogenicity sample for the given study day, and were followed for the entire duration of the study challenge period, or at least until MMID was observed

Blood samples were collected pre-challenge (Day -2) and post-challenge on Days 8, 29 and 61 for the MN assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. Seroconversion was defined as a pre-challenge titer 1:10 or greater and a minimum 4-fold rise in post-challenge antibody titer. The percentage of participants achieving seroconversion was calculated within each post-challenge study day and by infection status as observed over the study challenge period (Day 2 to Day 8); RT-PCR Negative (never positive), RT-PCR Positive Asymptomatic (participants with at least one positive PCR result but no symptoms reported), at least once RT-PCR Positive Symptomatic (or MMID).

Outcome measures

Outcome measures
Measure	Study Group n=75 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
Percentage of Healthy Participants Achieving MN Seroconversion From Baseline in Serum at Day 8 by Infection Status RT-PCR Positive Symptomatic	7.5 percentage of participants Interval 2.1 to 18.2
Percentage of Healthy Participants Achieving MN Seroconversion From Baseline in Serum at Day 8 by Infection Status RT-PCR Positive Asymptomatic	0 percentage of participants Interval 0.0 to 36.9
Percentage of Healthy Participants Achieving MN Seroconversion From Baseline in Serum at Day 8 by Infection Status RT-PCR Negative	0 percentage of participants Interval 0.0 to 23.2

SECONDARY outcome

Timeframe: Day 29

Population: All participants who received the study challenge, had an available immunogenicity sample for the given study day, and were followed for the entire duration of the study challenge period, or at least until MMID was observed

Blood samples were collected pre-challenge (Day -2) and post-challenge on Days 8, 29 and 61 for the MN assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. Seroconversion was defined as a pre-challenge titer 1:10 or greater and a minimum 4-fold rise in post-challenge antibody titer. The percentage of participants achieving seroconversion was calculated within each post-challenge study day and by infection status as observed over the study challenge period (Day 2 to Day 8); RT-PCR Negative (never positive), RT-PCR Positive Asymptomatic (participants with at least one positive PCR result but no symptoms reported), at least once RT-PCR Positive Symptomatic (or MMID).

Outcome measures

Outcome measures
Measure	Study Group n=67 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
Percentage of Healthy Participants Achieving MN Seroconversion From Baseline in Serum at Day 29 by Infection Status RT-PCR Positive Symptomatic	26.1 percentage of participants Interval 14.3 to 41.1
Percentage of Healthy Participants Achieving MN Seroconversion From Baseline in Serum at Day 29 by Infection Status RT-PCR Positive Asymptomatic	28.6 percentage of participants Interval 3.7 to 71.0
Percentage of Healthy Participants Achieving MN Seroconversion From Baseline in Serum at Day 29 by Infection Status RT-PCR Negative	0 percentage of participants Interval 0.0 to 23.2

SECONDARY outcome

Timeframe: Day 61

Population: All participants who received the study challenge, had an available immunogenicity sample for the given study day, and were followed for the entire duration of the study challenge period, or at least until MMID was observed

Blood samples were collected pre-challenge (Day -2) and post-challenge on Days 8, 29 and 61 for the MN assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. Seroconversion was defined as a pre-challenge titer 1:10 or greater and a minimum 4-fold rise in post-challenge antibody titer. The percentage of participants achieving seroconversion was calculated within each post-challenge study day and by infection status as observed over the study challenge period (Day 2 to Day 8); RT-PCR Negative (never positive), RT-PCR Positive Asymptomatic (participants with at least one positive PCR result but no symptoms reported), at least once RT-PCR Positive Symptomatic (or MMID).

Outcome measures

Outcome measures
Measure	Study Group n=62 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
Percentage of Healthy Participants Achieving MN Seroconversion From Baseline in Serum at Day 61 by Infection Status RT-PCR Positive Symptomatic	18.6 percentage of participants Interval 8.4 to 33.4
Percentage of Healthy Participants Achieving MN Seroconversion From Baseline in Serum at Day 61 by Infection Status RT-PCR Positive Asymptomatic	50 percentage of participants Interval 11.8 to 88.2
Percentage of Healthy Participants Achieving MN Seroconversion From Baseline in Serum at Day 61 by Infection Status RT-PCR Negative	0 percentage of participants Interval 0.0 to 24.7

SECONDARY outcome

Timeframe: Day 2 through Day 15

Population: All participants who received the study challenge, had a baseline sample for immunogenicity, and were followed for the entire duration of the study challenge period.

Blood samples were collected pre-challenge (Day -2) for the HAI assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. The geometric mean of each sample's replicate results was calculated from available results, then grouped by seroprotection status (titer results \>= 1:40 vs \< 1:40). Duration of viral shedding (detected by any approved positive RT-PCR test from NP swab) was calculated from the day of the initial positive PCR result to the day of the last positive PCR result prior to discharge from the challenge unit facility, regardless of intermittent negative PCR results. The mean duration of viral shedding was calculated among participants with detected virus within each pre-challenge HAI seroprotection status group.

Outcome measures

Outcome measures
Measure	Study Group n=61 Participants 2 mL (approximately 5x10\^6/mL tissue culture infective dose (TCID50)) of influenza A/Bethesda/MM2/H1N1 challenge virus administered intranasally via a sprayer on Day 1.
Duration of Viral Shedding in Nasopharyngeal (NP) Swab by Baseline HAI Seroprotection Status Low < 1:40	3.8 days Interval 2.9 to 4.7
Duration of Viral Shedding in Nasopharyngeal (NP) Swab by Baseline HAI Seroprotection Status High >= 1:40	2.3 days Interval 1.6 to 3.0

SECONDARY outcome

Timeframe: Day 2 to Day 15

Population: All participants who received the study challenge, had a baseline sample for immunogenicity, and were followed for the entire duration of the study challenge period.

Blood samples were collected pre-challenge (Day -2) for the MN assay conducted with the A/Bethesda/MM2/H1N1 virus as the antigen. The geometric mean of each sample's replicate results was calculated from available results, then grouped by seroprotection status (titer results \>= 1:40 vs \< 1:40). Duration of viral shedding (detected by any approved positive RT-PCR test from NP swab) was calculated from the day of the initial positive PCR result to the day of the last positive PCR result prior to discharge from the challenge unit facility, regardless of intermittent negative PCR results. The mean duration of viral shedding was calculated among participants with detected virus within each pre-challenge MN seroprotection status group.