Efficacy and Safety of Molnupiravir in Healthy Participants Inoculated With Experimental Influenza Virus (MK-4482-019)

Merck Sharp & Dohme LLC161 enrolled

Overview

This is a phase 2a double-blind, randomized, placebo-controlled study to evaluate the efficacy and safety of molnupiravir (MK-4482) in healthy participants inoculated with experimental influenza virus. The primary hypotheses are that MK-4482 initiated 12 hours following intranasal inoculation of the influenza challenge virus reduces the peak viral load compared to placebo and that MK-4482 initiated 2 days following intranasal inoculation of the influenza challenge virus reduces the viral load area under the curve (AUC) compared to placebo.

This study has two parts. Part 1 is an open-label validation study, with a cohort of 20 untreated participants undergoing nasal inoculation with the A/France/759/21 \[H1N1\] strain on Day 0 to confirm viral infectivity and disease. Part 2 will be a randomized, double-blind placebo- and active-comparator-controlled study where participants will be inoculated on Day 0 with either the A/France/759/21 \[H1N1\] virus used in Part 1 or an alternative influenza virus. Part 2 will evaluate the antiviral efficacy, pharmacokinetics, and safety of MK-4482 in participants inoculated with the challenge virus.

Study Type

INTERVENTIONAL

Allocation

RANDOMIZED

Purpose

TREATMENT

Masking

DOUBLE

Enrollment

161

Conditions

Influenza Infection

Interventions

MolnupiravirDRUG

Four molnupiravir 200 mg capsules (800 mg total dose) taken twice daily by mouth.

Placebo molnupiravirDRUG

Four placebo capsules matched to molnupiravir taken twice daily by mouth.

Placebo oseltamivirDRUG

Placebo capsule matched to oseltamivir taken twice daily by mouth.

OseltamivirDRUG

One capsule of oseltamivir 75 mg taken twice daily by mouth.

Influenza A VirusBIOLOGICAL

Influenza A challenge virus given once by intranasal administration at an inoculum concentration of between approximately 5 and 7 Log10 tissue culture infective dose 50% (TCID50/mL).

Eligibility

Sex: ALLMin age: 18 YearsMax age: 55 YearsHealthy volunteers:

Medical Language ↔ Plain English

Inclusion Criteria: * Is in good health based on medical history, physical examination, vital sign measurements, spirometry, and electrocardiograms performed before inoculation. * Has a total body weight ≥50 kg and Body Mass Index (BMI) ≥18 kg/m\^2 and ≤35 kg/m\^2. * For males: abstains from heterosexual intercourse as their preferred and usual lifestyle and agrees to remain abstinent OR uses contraception unless confirmed to be azoospermic. * For participants assigned female sex at birth: is not pregnant or breastfeeding, AND is either not a person of childbearing potential (POCBP) or is a POCBP AND uses a contraceptive method that is highly effective (low user dependency method, OR a user dependent hormonal method in combination with barrier method), or is abstinent from penile-vaginal intercourse as their preferred and usual lifestyle, has a negative highly sensitive pregnancy test, abstains from breastfeeding, and has medical, menstrual, and recent sexual activity history reviewed by the investigator to decrease risk of early undetected pregnancy. Exclusion Criteria: * Has a history of, or has currently active, symptoms or signs suggestive of upper or lower respiratory tract infection within 4 weeks prior to admission to quarantine. * Has a history of clinically significant endocrine, gastrointestinal (GI), cardiovascular, hematological, hepatic, immunological, renal, respiratory, genitourinary, or major neurological abnormalities or diseases. * Is mentally or legally incapacitated, has significant emotional problems at the time of prestudy visit, or expected during the conduct of the study, or has a history of clinically significant psychiatric disorder of the last 5 years. * Has a history of cancer. * Has a history of rhinitis which is clinically active, or history of moderate to severe rhinitis, or history of seasonal allergic rhinitis likely to be active at the time of inclusion into the study and/or requiring regular nasal corticosteroids on an at least weekly basis, within 30 days prior to admission to quarantine. * Has a history of atopic dermatitis/eczema which is clinically severe and/or requiring moderate to large amounts of daily dermal corticosteroids. * Has a diagnosis of cluster headache/migraine or is receiving prophylaxis against migraine. * Has a lifetime history of anaphylaxis and/or a lifetime history of severe allergic reaction. Significant intolerance to any food or drug in the last 12 months. * Has had major surgery and/or donated or lost 1 unit of blood within 3 months prior to the prestudy visit. * Uses or anticipates the use of concomitant medications, including vitamins or herbal and dietary supplements from approximately 2 weeks prior to the planned date of viral challenge until the poststudy visit. * Has evidence of receipt of vaccine within the 4 weeks prior to the planned date of viral challenge. * Intends to receive any vaccine(s) before the last day of follow-up. * Has received any investigational drug within 3 months prior to the planned date of viral challenge. * Has received 3 or more investigational drugs within the previous 12 months prior to the planned date of viral challenge. * Has had prior inoculation with a virus from the same virus subtype as the challenge virus. * Has had prior inoculation with a virus from the same virus-family as the challenge virus in the last 12 months. * Has had prior participation in another human viral challenge study with a respiratory virus in the preceding 3 months, taken from the date of viral challenge in the previous study to the date of expected viral challenge in this study. * Has smoked ≥10 pack-years at any time. * Has a recent history or presence of alcohol addiction, or excessive use of alcohol. * Consumes excessive amounts, defined as more than 6 servings of caffeinated beverages or xanthine-containing products. * Has any significant abnormality altering the anatomy of the nose in a substantial way or nasopharynx that may interfere with the aims of the study and, in particular, any of the nasal assessments or viral challenge. * Has any clinically significant history of epistaxis. * Has had any nasal or sinus surgery within 3 months. * Is a regular user of cannabis or any illicit drugs, or has a history of drug abuse within approximately 1 year.

Locations (1)

hVIVO Services ( Site 0001)

London, London, City of, United Kingdom

Outcomes

Primary Outcomes

Part 1: Infectivity Rate Based on Quantitative Reverse Transcriptase-Polymerase Chain Reaction (qRT-PCR) From Day 1 PM Through Day 8 AM

Infectivity rate was defined as the number of participants with two quantifiable (≥lower limit of quantitation (LLOQ)) influenza challenge virus (A/France/759/21 \[H1N1\] strain) qRT-PCR measurements reported on ≥2 independent nasopharyngeal samples (from nasal wash samples collected twice daily - morning and evening). Infectivity rate based on qRT-PCR in Part 1 participants from baseline (day 1 PM - afternoon) up to planned discharge from quarantine (day 8 AM - post viral inoculation) is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 1: Infectivity Rate Based on Quantitative Reverse Transcriptase-Polymerase Chain Reaction (qRT-PCR) From Day 2 PM Through Day 8 AM

The number of participants with two quantifiable (≥lower limit of quantitation (LLOQ)) influenza challenge virus qRT-PCR measurements reported on ≥2 independent nasopharyngeal samples (from nasal wash samples collected twice daily - morning and evening). Infectivity rate based on qRT-PCR in Part 1 participants from day 2 PM up to day 8 post viral inoculation is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 2 PM up to Day 8 post viral inoculation

Part 1: Number of Participants Experiencing ≥1 Viral Challenge-related Adverse Event (AE)

An AE is 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. An AE is viral challenge-related as determined by the investigator. Number of participants experiencing ≥1 viral challenge-related AE in part 1 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: Up to approximately 31 days

Part 2: Peak Viral Load (PVL) Determined by Quantitative Viral Culture Tissue Culture Infective Dose 50% (TCID50) Assay From Day 1 PM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

PVL was defined as the maximum viral load of influenza challenge virus from nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening). PVL as determined by quantitative viral culture (QVC) was measured starting from day 1 PM (baseline) up to planned discharge from quarantine (day 8 AM). PVL of the H1N1 strain was measured by quantitative viral culture (QVC) using TCID50 plaque assay and analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Area Under the Viral Load-Time Curve (VL-AUC) Determined by QVC (TCID50 Assay) From Day 2 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx and Placebo)

VL-AUC is the area under the viral load-time curve of influenza challenge virus nasopharyngeal samples determined by QVC. H1N1 viral load was computed for each participant from nasopharyngeal samples collected twice daily (morning and evening) from day 2 AM to day 8 AM. VL-AUC (on the log10 scale) was analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for Molnupiravir Tx and placebo were presented for this endpoint.

Time frame: Days 2, 3, 4, 5, 6, 7 - twice daily (AM and PM), and day 8 AM post viral inoculation

Secondary Outcomes

Part 1: QVC-Confirmed Influenza Infection From Day 1 PM Through Day 8 AM After Intranasal Inoculation

QVC-Confirmed Influenza Infection was defined as the number of participants with one quantifiable ≥LLOQ influenza challenge virus measurement from QVC (plaque assay) of nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening). QVC confirmed influenza infection in Part 1 participants from day 1 PM up to day 8 post viral inoculation is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 1: QVC-Confirmed Influenza Infection From Day 2 PM Through Day 8 AM After Intranasal Inoculation

QVC-Confirmed Influenza Infection was defined as the number of participants with one quantifiable ≥LLOQ influenza challenge virus measurement from QVC (plaque assay) of nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening). QVC confirmed influenza infection in Part 1 participants from day 2 PM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 2 PM Up to Day 8 post viral inoculation

Part 1: VL-AUC Determined by qRT-PCR From Day 1 PM Through Day 8 AM After Intranasal Inoculation

VL-AUC is the area under the viral load-time curve of influenza challenge virus nasopharyngeal samples determined by qRT-PCR. H1N1 viral load was computed for each participant from nasopharyngeal samples collected twice daily (morning and evening) from day 1 PM to day 8 AM. VL-AUC (on the log10 scale) was analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: Day 1 PM, Days 2, 3, 4, 5, 6, 7 - twice daily (AM and PM), and day 8 AM post viral inoculation

Part 1: VL-AUC Determined by qRT-PCR From Day 2 PM Through Day 8 AM After Intranasal Inoculation

VL-AUC is the area under the viral load-time curve of influenza challenge virus nasopharyngeal samples determined by qRT-PCR. H1N1 viral load was computed for each participant from nasopharyngeal samples collected twice daily (morning and evening) from day 2 PM to day 8 AM. VL-AUC (on the log10 scale) was analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for part 1 participants were presented for this endpoint. VL-AUC by qRT-PCR in Part 1 participants from day 2 PM up to day 8 is presented.

Data from ClinicalTrials.gov

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Time frame: Day 2 PM, Days 3, 4, 5, 6, 7 - twice daily (AM and PM), and day 8 AM post viral inoculation

Part 1: VL-AUC Determined by Quantitative Viral Culture (TCID50 Assay) From Day 1 PM Through Day 8 AM After Intranasal Inoculation

VL-AUC is the area under the viral load-time curve of influenza challenge virus nasopharyngeal samples determined by QVC. H1N1 viral load was computed for each participant from nasophayngeal samples collected twice daily (morning and evening) from day 1 PM to day 8 AM. VL-AUC (on the log10 scale) was analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for part 1 participants were presented for this endpoint. VL-AUC by QVC in Part 1 participants from day 1 PM up to day 8 is presented.

Time frame: Day 1 PM, Days 2, 3, 4, 5, 6, 7 - twice daily (AM and PM), and day 8 AM post viral inoculation

Part 1: VL-AUC Determined by Quantitative Viral Culture (TCID50 Assay) From Day 2 PM Through Day 8 AM After Intranasal Inoculation

VL-AUC is the area under the viral load-time curve of influenza challenge virus nasopharyngeal samples determined by QVC. H1N1 viral load was computed for each participant from nasopharyngeal samples collected twice daily (morning and evening) from day 1 PM to day 8 AM. VL-AUC (on the log10 scale) was analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for part 1 participants were presented for this endpoint. VL-AUC by QVC in Part 1 participants from day 2 PM up to day 8 is presented.

Time frame: Day 2 PM, Days 3, 4, 5, 6, 7 - twice daily (AM and PM), and day 8 AM post viral inoculation

Part 1: PVL Determined by qRT-PCR From Day 1 PM Through Day 8 AM After Intranasal Inoculation

PVL was defined as the maximum viral load of influenza challenge virus from nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening) from day 1 PM (baseline) through day 8 AM. PVL of the H1N1 strain was measured by qRT-PCR and analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 1: PVL Determined by qRT-PCR From Day 2 PM Through Day 8 AM After Intranasal Inoculation

PVL was defined as the maximum viral load of influenza challenge virus from nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening) from day 2 PM (baseline) through day 8 AM. PVL of the H1N1 strain was measured by qRT-PCR and analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 2 PM up to Day 8 post viral inoculation

Part 1: PVL Determined by Quantitative Viral Culture (TCID50 Assay) From Day 1 PM Through Day 8 AM After Intranasal Inoculation

PVL was defined as the maximum viral load of influenza challenge virus from nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening) from day 1 PM (baseline) through day 8 AM. PVL of the H1N1 strain was measured by QVC and analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 1: PVL Determined by Quantitative Viral Culture (TCID50 Assay) From Day 2 PM Through Day 8 AM After Intranasal Inoculation

PVL was defined as the maximum viral load of influenza challenge virus from nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening) from day 2 PM (baseline) through day 8 AM. PVL of the H1N1 strain was measured by QVC and analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 2 PM up to Day 8 post viral inoculation

Part 1: Duration in Days of Quantifiable Influenza Infection by qRT-PCR From Day 1 PM Through Day 8 AM After Intranasal Inoculation

Duration in days of quantifiable influenza infection was defined as the time in days from the first quantifiable (≥LLOQ) influenza challenge virus measurement until the first confirmed unquantifiable (\<LLOQ detected or not detected) assessment after the peak measure (after which there are no more confirmed quantifiable samples) determined by qRT-PCR from nasal wash samples collected twice daily (morning and evening). Duration of Quantifiable Influenza by qRT-PCR in Part 1 participants from day 1 PM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 1: Duration in Days of Quantifiable Influenza Infection by qRT-PCR From Day 2 PM Through Day 8 AM After Intranasal Inoculation

Duration in days of quantifiable influenza infection was defined as the time in days from the first quantifiable (≥LLOQ) influenza challenge virus measurement until the first confirmed unquantifiable (\<LLOQ detected or not detected) assessment after the peak measure after which there are no more confirmed quantifiable samples) determined by qRT-PCR from nasal wash samples collected twice daily (morning and evening). Duration of Quantifiable Influenza by qRT-PCR in Part 1 participants from day 2 PM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 2 PM up to Day 8 post viral inoculation

Part 1: Duration in Days of Quantifiable Influenza Infection by QVC (TCID50 Assay) Confirmed Infection From Day 1 PM Through Day 8 AM After Intranasal Inoculation

Duration in days of quantifiable influenza infection was defined as the time in days from the first quantifiable (≥LLOQ) influenza challenge virus measurement until the first confirmed unquantifiable (\<LLOQ detected or not detected) assessment after the peak measure after which there are no more confirmed quantifiable samples) determined by QVC (plaque assay) from nasal wash samples collected twice daily (morning and evening). Duration of Quantifiable Influenza by QVC in Part 1 participants from day 1 PM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 1: Duration in Days of Quantifiable Influenza Infection by QVC Confirmed Infection From Day 2 PM Through Day 8 AM After Intranasal Inoculation

Duration in days of quantifiable influenza infection was defined as the time in days from the first quantifiable (≥LLOQ) influenza challenge virus measurement until the first confirmed unquantifiable (\<LLOQ detected or not detected) assessment after the peak measure after which there are no more confirmed quantifiable samples) determined by QVC (plaque assay) from nasal wash samples collected twice daily (morning and evening). Duration of Quantifiable Influenza by QVC in Part 1 participants from day 2 PM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 2 PM up to Day 8 post viral inoculation

Part 1: Area Under the Total Symptom Score-Time Curve (TSS-AUC) From Day 1 AM Through Day 8 AM After Intranasal Inoculation

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom was used to obtain a total symptom score (TSS). TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. TSS were used to calculate the AUC for each participant based on the available non-missing calculated total symptom scores between Day 1 until Day 8 (quarantine discharge) using the Trapezoidal rule. TSS-AUC measured from 10 symptoms assessed 3 times daily within the graded symptom scoring was reported. TSS-AUC in Part 1 participants from day 1 AM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 1 AM up to Day 8 post viral inoculation

Part 1: Area Under the Total Symptom Score-Time Curve (TSS-AUC) From Day 2 AM Through Day 8 AM After Intranasal Inoculation

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom was used to obtain TSS. Total symptom scores (TSS) ranged from 0 to 31, with higher scores indicating greater symptom severity. TSS were used to calculate the AUC for each participant based on the available non-missing calculated total symptom scores between Day 2 until Day 8 (quarantine discharge) using the Trapezoidal rule. TSS-AUC in Part 1 participants from day 2 AM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 1: Peak Total Symptom Score (TSS) From Day 1 AM Through Day 8 AM After Intranasal Inoculation

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom was used to obtain a total symptom score (TSS). TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. The highest TSS (defined as the sum of all 10 individual composite symptoms) was summarized by treatment group and analyzed using a linear model with treatment group as a fixed categorical effect. Peak TSS measured from 10 symptoms within the graded symptom scoring system collected 3 times daily was reported. Peak TSS in Part 1 participants from day 1 AM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 1 AM up to Day 8 post viral inoculation

Part 1: Peak Total Symptom Score (TSS) From Day 2 AM Through Day 8 AM After Intranasal Inoculation

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom was used to obtain TSS. TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. The highest TSS (defined as the sum of all 10 individual composite symptoms) was summarized by treatment group and analyzed using a linear model with treatment group as a fixed categorical effect. Peak TSS measured from 10 symptoms within the graded symptom scoring system collected 3 times daily was reported. Peak TSS in Part 1 participants from day 2 AM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 1: Daily Maximum TSS From Day 1 AM Through Day 8 AM After Intranasal Inoculation

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom was used to obtain TSS. TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. Maximum TSS on each day, measured by graded symptom scoring system collected 3 times daily were reported. Daily maximum TSS in Part 1 participants from day 1 AM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 1 AM up to Day 8 post viral inoculation

Part 1: Duration in Days of Grade ≥2 Symptoms From Day 1 AM Through Day 8 AM After Intranasal Inoculation

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from Grade 0 ("no symptoms") to Grade 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from Grade 0 ("no symptoms") to Grade 4 ("symptoms at rest"). Duration of Grade 2 symptoms is defined as the duration in days from the first occurrence of a Grade 2 or higher symptom until the first 24 hours period where no Grade 2 or higher symptoms are recorded. Duration in days of grade ≥2 Symptoms in part 1 participants from day 1 AM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 1 AM up to Day 8 post viral inoculation

Part 1: Duration of Grade ≥2 Symptoms From Day 2 AM Through Day 8 AM After Intranasal Inoculation

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from Grade 0 ("no symptoms") to Grade 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from Grade 0 ("no symptoms") to Grade 4 ("symptoms at rest"). Duration of Grade 2 symptoms is defined as the duration in days from the first occurrence of a Grade 2 or higher symptom until the first 24 hours period where no Grade 2 or higher symptoms are recorded. Duration in days of grade ≥2 Symptoms in part 1 participants from day 2 AM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 1: Time to Symptom Resolution From Day 1 AM Through Day 8 AM After Intranasal Inoculation

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. Time in days to symptom resolution was defined as the time in days from the beginning of the specified time frame until the beginning of a 24-hour period with no symptoms above the baseline maximum TSS, as measured by graded symptom scoring system collected 3 times daily. Baseline maximum is defined as the maximum TSS on Day -1 (1 day prior to intranasal inoculation). Time in days to symptom resolution in part 1 participants from day 1 AM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 1 AM up to Day 8 post viral inoculation

Part 1: Time to Symptom Resolution From Day 2 AM Through Discharge From Quarantine (Day 8 AM) After Intranasal Inoculation

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. Time in days to symptom resolution was defined as the time (in days) from the beginning of the specified time frame until the beginning of a 24-hour period with no symptoms above the baseline maximum TSS, as measured by graded symptom scoring system collected 3 times daily. Baseline maximum is defined as the maximum TSS on Day -1 (1 day prior to intranasal inoculation). Time in days to symptom resolution in part 1 participants from day 2 AM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 1: Time to Peak TSS From Day 1 AM Through Day 8 AM After Intranasal Inoculation

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom was used to obtain TSS. TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. The highest total symptom score recorded on each day, across the three assessments, for each participant was summarized descriptively by treatment group and assessment day. Time to peak TSS was defined as the time from the assessment at Day 1 AM until the highest total symptom score was calculated. Time to peak TSS in Part 1 participants from day 1 AM up to day 8 is presented. Per protocol, only data for part 1 participants were presented for this endpoint.

Time frame: From Day 1 AM up to Day 8 post viral inoculation

Part 2: VL-AUC Determined by qRT-PCR From Day 1 PM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

VL-AUC is the area under the viral load-time curve of influenza challenge virus nasopharyngeal samples determined by qRT-PCR. H1N1 viral load was computed for each participant from nasopharyngeal samples collected twice daily (morning and evening) from day 1 PM to day 8 AM. VL-AUC (on the log10 scale) was analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: Day 1 PM, Days 2, 3, 4, 5, 6, 7 - twice daily (AM and PM), and day 8 AM post viral inoculation

Part 2: VL-AUC Determined by Quantitative Viral Culture (TCID50 Assay) From Day 1 PM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

VL-AUC is the area under the viral load-time curve of influenza challenge virus nasopharyngeal samples determined by QVC. H1N1 viral load was computed for each participant from nasophayngeal samples collected twice daily (morning and evening) from day 1 PM to day 8 AM. VL-AUC (on the log10 scale) was analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: Day 1 PM, Days 2, 3, 4, 5, 6, 7 - twice daily (AM and PM), and day 8 AM post viral inoculation

Part 2: PVL Determined by qRT-PCR From Day 1 PM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

PVL was defined as the maximum viral load of influenza challenge virus from nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening) from day 1 PM (baseline) through day 8 AM. PVL of the H1N1 strain was measured by qRT-PCR and analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Percentage of Participants With qRT-PCR-Confirmed Influenza Infection From Day 1 PM up to Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Percentage of Participants With qRT-PCR-Confirmed Symptomatic Influenza Infection From Day 1 PM up to Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

The percentage of participants with two quantifiable (≥ LLOQ) influenza challenge virus qRT-PCR measurements reported on ≥2 independent nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening) within 48 h of each other, starting from baseline (Day 1 PM) up to planned discharge from quarantine (Day 8, AM) AND total symptom score (TSS) ≥2 at ≥1 time point following inoculation. Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom is used to obtain TSS. Total symptom scores (TSS) ranged from 0 to 31, with higher scores indicating greater symptom severity. Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Percentage of Participants With qRT-PCR-Confirmed Moderately Severe Symptomatic Influenza Infection From Day 1 PM up to Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

The percentage of participants with two quantifiable (≥ LLOQ) influenza challenge virus qRT-PCR measurements reported on ≥2 independent nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening) over 2 days AND any symptom of Grade ≥2 at ≥1 timepoint following inoculation. Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from Grade 0 ("no symptoms") to Grade 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from Grade 0 ("no symptoms") to Grade 4 ("symptoms at rest"). Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Percentage of Participants With qRT-PCR-Confirmed Febrile Influenza Infection From Day 1 PM up to Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

Percentage of participants with qRT-PCR-confirmed febrile influenza infection was defined as the percentage of participants with two quantifiable (≥ LLOQ) influenza challenge virus qRT-PCR measurements reported on ≥2 independent nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening) over 2 days, starting from baseline (Day 1 PM) up to planned discharge from quarantine (Day 8, am) AND a temperature of ≥37.9°C at ≥1 time point following inoculation. Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Percentage of Participants With QVC Confirmed Influenza Infection From Day 1 PM up to Day 8 AM After Intranasal Inoculations (Molnupiravir PEP and Placebo)

Percentage of participants with QVC confirmed influenza infection was defined as the percentage of participants with one quantifiable ≥LLOQ influenza challenge virus measurement from QVC (TCID50 assay) from a nasopharyngeal sample (nasal wash samples collected twice daily - morning and evening). Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Percentage of Participants With QVC Confirmed Symptomatic Influenza Infection From Day 1 PM up to Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

Percentage of participants with QVC (TCID50 assay) confirmed symptomatic influenza infection was defined as the percentage of participants with one quantifiable ≥LLOQ influenza challenge virus measurement from quantitative viral culture from a nasopharyngeal sample (nasal wash samples collected twice daily - morning and evening) AND TSS ≥2 at ≥1 time point following inoculation. Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom is used to obtain a total symptom score (TSS). TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Duration of Quantifiable Infection Determined by qRT-PCR From Day 1 PM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

Duration of quantifiable infection was defined as the time in days from the first quantifiable (≥LLOQ) influenza challenge virus measurement until the first confirmed unquantifiable (\<LLOQ detected or not detected) assessment after the peak measure (after which there are no more confirmed quantifiable samples) determined by qRT-PCR. Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Duration of Quantifiable Infection Determined by QVC From Day 1 PM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

Duration of quantifiable infection was defined as the time in days from the first quantifiable (≥LLOQ) influenza challenge virus measurement until the first confirmed unquantifiable (\<LLOQ detected or not detected) assessment after the peak measure after which there are no more confirmed quantifiable samples) determined by QVC (TCID50 assay). Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Time to Confirmed Negative Test Determined by qRT-PCR From Day 1 PM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

Time to confirmed negative test was defined as the time in days from baseline until the first confirmed unquantifiable (\<LLOQ detected or not detected) assessment after the peak measure (after which there are no more confirmed quantifiable samples) as determined by qRT-PCR from nasal wash samples collected twice daily (morning and evening). Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Time to Confirmed Negative Test Determined by QVC (TCID50 Assay) From Day 1 PM Through Day 8 AM After Intranasal Inoculations (Molnupiravir PEP and Placebo)

Time to confirmed negative test was defined as the time in days from baseline until the first confirmed unquantifiable (\<LLOQ detected or not detected) assessment after the peak measure (after which there are no more confirmed quantifiable samples) as determined by QVC (TCID50 assay) from nasal wash samples collected twice daily (morning and evening). Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Time to PVL Determined by qRT-PCR From Day 1 PM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

Time to PVL was defined as the time in days from the baseline until the PVL measurement as determined by qRT-PCR from nasal wash samples collected twice daily (morning and evening). PVL was defined as the maximum viral load of influenza challenge virus from nasopharyngeal samples. Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: From Day 1 PM Up to Day 8 post viral inoculation

Part 2: Time to PVL Determined by QVC From Day 1 PM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

Time to PVL was defined as the time in days from the baseline until the PVL measurement as determined by QVC (TCID50 assay) from nasal wash samples collected twice daily (morning and evening). PVL was defined as the maximum viral load of influenza challenge virus from nasopharyngeal samples. Per protocol, only data for Molnupiravir PEP and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: VL-AUC Determined by qRT-PCR From Day 1 PM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx and Placebo)

VL-AUC is the area under the viral load-time curve of influenza challenge virus nasopharyngeal samples determined by qRT-PCR. H1N1 viral load was computed for each participant from nasophayngeal samples collected twice daily (morning and evening) from day 1 PM to day 8 AM. VL-AUC (on the log10 scale) was analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for Molnupiravir Tx and placebo were presented for this endpoint.

Time frame: Day 1 PM, Days 2, 3, 4, 5, 6, 7 - twice daily (AM and PM), and day 8 AM post viral inoculation

Part 2: VL-AUC Determined by qRT-PCR From Day 1 PM Through Day 8 AM After Intranasal Inoculation (OTV Tx and Placebo)

VL-AUC is the area under the viral load-time curve of influenza challenge virus nasopharyngeal samples determined by qRT-PCR. H1N1 viral load was computed for each participant from nasophayngeal samples collected twice daily (morning and evening) from day 1 PM to day 8 AM. VL-AUC (on the log10 scale) was analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for OTV Tx and placebo were presented for this endpoint.

Time frame: Day 1 PM, Days 2, 3, 4, 5, 6, 7 - twice daily (AM and PM), and day 8 AM post viral inoculation

Part 2: VL-AUC Determined by Quantitative Viral Culture (TCID50 Assay) From Day 1 PM Through Discharge Day 8 AM After Intranasal Inoculation (Molnupiravir Tx and Placebo)

VL-AUC is the area under the viral load-time curve of influenza challenge virus nasopharyngeal samples determined by QVC. H1N1 viral load was computed for each participant from nasophayngeal samples collected twice daily (morning and evening) from day 1 PM to day 8 AM. VL-AUC (on the log10 scale) was analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for Molnupiravir Tx and placebo were presented for this endpoint.

Time frame: Day 1 PM, Days 2, 3, 4, 5, 6, 7 - twice daily (AM and PM), and day 8 AM post viral inoculation

Part 2: VL-AUC Determined by Quantitative Viral Culture (TCID50 Assay) From Day 1 PM Through Day 8 AM After Intranasal Inoculation (OTV Tx and Placebo)

VL-AUC is the area under the viral load-time curve of influenza challenge virus nasopharyngeal samples determined by QVC. H1N1 viral load was computed for each participant from nasopharyngeal samples collected twice daily (morning and evening) from day 1 PM to day 8 AM. VL-AUC (on the log10 scale) was analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for OTV Tx and placebo were presented for this endpoint.

Time frame: Day 1 PM, Days 2, 3, 4, 5, 6, 7 - twice daily (AM and PM), and day 8 AM post viral inoculation

Part 2: PVL Determined by Quantitative Viral Culture (TCID50 Assay) From Day 1 PM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx and Placebo)

PVL was defined as the maximum viral load of influenza challenge virus from nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening). PVL as determined by quantitative viral culture (QVC) was measured starting from day 1 PM (baseline) up to planned discharge from quarantine (day 8 AM). PVL of the H1N1 strain was measured by quantitative viral culture (QVC) using TCID50 assay and analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for Molnupiravir Tx and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: PVL Determined by Quantitative Viral Culture (TCID50 Assay) From Day 1 PM Through Day 8 AM After Intranasal Inoculation (OTV Tx and Placebo)

PVL was defined as the maximum viral load of influenza challenge virus from nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening). PVL as determined by quantitative viral culture (QVC) was measured starting from day 1 PM (baseline) up to planned discharge from quarantine (day 8 AM). PVL of the H1N1 strain was measured by quantitative viral culture (QVC) using TCID50 assay and analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for OTV Tx and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: PVL Determined by qRT-PCR From Day 1 PM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx and Placebo)

PVL was defined as the maximum viral load of influenza challenge virus from nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening) from day 1 PM (baseline) through day 8 AM. PVL of the H1N1 strain was measured by qRT-PCR and analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for Molnupiravir Tx and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: PVL Determined by qRT-PCR From Day 1 PM Through Day 8 AM After Intranasal Inoculation (OTV Tx and Placebo)

PVL was defined as the maximum viral load of influenza challenge virus from nasopharyngeal samples (nasal wash samples collected twice daily - morning and evening) from day 1 PM (baseline) through day 8 AM. PVL of the H1N1 strain was measured by qRT-PCR and analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only data for OTV Tx and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Duration of Quantifiable Infection Determined by qRT-PCR From Day 2 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx, OTV Tx and Placebo)

Duration of quantifiable infection was defined as the time from the first quantifiable (≥LLOQ) influenza challenge virus measurement until the first confirmed unquantifiable (\<LLOQ detected or not detected) assessment after the peak measure (after which there are no more confirmed quantifiable samples) determined by qRT-PCR. Per protocol, only data for Molnupiravir Tx, OTV Tx and placebo were presented for this endpoint.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 2: Duration of Quantifiable Infection Determined by QVC From Day 2 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx, OTV Tx and Placebo)

Time from the first quantifiable (≥LLOQ) influenza challenge virus measurement until the first confirmed unquantifiable (\<LLOQ detected or not detected) assessment after the peak measure after which there are no more confirmed quantifiable samples) determined by QVC (TCID50 assay). Per protocol, only data for Molnupiravir Tx, OTV Tx and placebo were presented for this endpoint.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 2: Time to Confirmed Negative Test Determined by qRT-PCR From Day 2 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx and Placebo)

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 2: Time to Confirmed Negative Test Determined by qRT-PCR From Day 1 PM Through Day 8 AM After Intranasal Inoculation (OTV Tx and Placebo)

Time to confirmed negative test was defined as the time in days from baseline until the first confirmed unquantifiable (\<LLOQ detected or not detected) assessment after the peak measure (after which there are no more confirmed quantifiable samples) as determined by qRT-PCR from nasal wash samples collected twice daily (morning and evening). Per protocol, only data for OTV Tx and placebo were presented for this endpoint.

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Time in Days to Confirmed Negative Test Determined by QVC From Day 2 AM Through Day 8 AM After Intranasal Inoculations (Molnupiravir Tx and Placebo)

Time to confirmed negative test was defined as the time in days from baseline until the first confirmed unquantifiable (\<LLOQ detected or not detected) assessment after the peak measure (after which there are no more confirmed quantifiable samples) as determined by QVC (TCID50 assay) from nasal wash samples collected twice daily (morning and evening). Per protocol, only data for Molnupiravir Tx and placebo were presented for this endpoint.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 2: Time in Days to Confirmed Negative Test Determined by QVC From Day 2 AM Through Day 8 AM After Intranasal Inoculation (OTV Tx and Placebo)

Time to confirmed negative test was defined as the time from baseline until the first confirmed unquantifiable (\<LLOQ detected or not detected) assessment after the peak measure (after which there are no more confirmed quantifiable samples) as determined by QVC (TCID50 assay) from nasal wash samples collected twice daily (morning and evening). Per protocol, only data for OTV Tx and placebo were presented for this endpoint.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 2: Time to PVL Determined by qRT-PCR From Day 1 PM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx, OTV Tx and Placebo)

Time frame: From Day 1 PM up to Day 8 post viral inoculation

Part 2: Time to PVL Determined by QVC From Day 2 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx, OTV and Placebo)

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 2: Total Symptom Score AUC (TSS-AUC) From Day 2 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx and Placebo)

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom was used to obtain TSS. Total symptom scores (TSS) ranged from 0 to 31, with higher scores indicating greater symptom severity. TSS were used to calculate the AUC for each participant based on the available non-missing calculated total symptom scores between Day 2 until Day 8 (quarantine discharge) using the Trapezoidal rule. TSS-AUC measured from 10 symptoms assessed 3 times daily within the graded symptom scoring was reported. Per protocol, only Molnupiravir Tx and placebo were included in the model.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 2: Total Symptom Score AUC (TSS-AUC) From Day 2 AM Through Day 8 AM After Intranasal Inoculation (OTV Tx and Placebo)

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). Total symptom scores (TSS) ranged from 0 to 31, with higher scores indicating greater symptom severity. For each participant, the sum of grade values for each symptom was used to obtain a total symptom score (TSS). TSS were used to calculate the AUC for each participant based on the available non-missing calculated total symptom scores between Day 2 until Day 8 (quarantine discharge) using the Trapezoidal rule. TSS-AUC was analyzed using a linear model with treatment group as a fixed categorical effect. Per protocol, only OTV Tx and placebo were included in the model. TSS-AUC measured from 10 symptoms within the graded symptom scoring was reported.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 2: Peak TSS From Day 2 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx and Placebo)

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom was used to obtain TSS. TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. The highest TSS (defined as the sum of all 10 individual composite symptoms) was summarized by treatment group and analyzed using a linear model with treatment group as a fixed categorical effect. Peak TSS measured from 10 symptoms within the graded symptom scoring system collected 3 times daily was reported. Per protocol, only Molnupiravir Tx and placebo were reported for this endpoint.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 2: Peak TSS From Day 2 AM Through Day 8 AM After Intranasal Inoculation (OTV Tx and Placebo)

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom was used to obtain TSS. TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. The highest TSS (defined as the sum of all 10 individual composite symptoms) was summarized by treatment group and analyzed using a linear model with treatment group as a fixed categorical effect. Peak TSS measured from 10 symptoms within the graded symptom scoring system collected 3 times daily was reported was reported. Per protocol, only OTV Tx and Placebo were reported for this endpoint.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 2: Daily Maximum TSS From Day 2 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx, OTV Tx and Placebo)

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 2: Daily Maximum TSS From Day 1 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

Time frame: From Day 1 AM up to Day 8 post viral inoculation

Part 2: Duration of Grade ≥2 Symptoms From Day 2 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx, OTV Tx and Placebo)

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from Grade 0 ("no symptoms") to Grade 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from Grade 0 ("no symptoms") to Grade 4 ("symptoms at rest"). Duration in days of Grade ≥2 symptoms was defined as the duration of time in days from the first occurrence of any symptom assigned Grade 2 or higher, to the beginning of the first 24-hour period without any symptom assigned Grade 2 or higher, after the peak TSS. Per protocol, Molnupiravir Tx, OTV Tx and Placebo were included in the analysis.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 2: Time to Symptom Resolution From Day 2 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx, OTV Tx and Placebo)

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. Time in days to symptom resolution was defined as the time in days until the beginning of a 24-hour period with no symptoms above the baseline maximum TSS, as measured by graded symptom scoring system collected 3 times daily. Baseline maximum is defined as the maximum TSS on Day -1 (1 day prior to intranasal inoculation). Per protocol, only Molnupiravir Tx, OTV Tx and Placebo were presented for this endpoint.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 2: Time to Peak TSS From Day 2 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir Tx, OTV Tx and Placebo)

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom was used to obtain TSS. TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. The highest total symptom score recorded on each day, across the three assessments, for each participant was summarized descriptively by treatment group and assessment day. Time to peak TSS was defined as the time from the assessment at Day 2 AM until the highest total symptom score was calculated. Per protocol, only Molnupiravir Tx, OTV Tx and Placebo were presented for this endpoint.

Time frame: From Day 2 AM up to Day 8 post viral inoculation

Part 2: Total Symptom Score AUC (TSS-AUC) From Day 1 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom was used to obtain TSS. Total symptom scores (TSS) ranged from 0 to 31, with higher scores indicating greater symptom severity. TSS were used to calculate the AUC for each participant based on the available non-missing calculated total symptom scores between Day 1 until Day 8 (quarantine discharge) using the Trapezoidal rule. Per protocol, only Molnupiravir PEP and Placebo was included in the model.

Time frame: From Day 1 AM up to Day 8 post viral inoculation

Part 2: Peak TSS From Day 1 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom is used to obtain TSS. TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. The highest TSS (defined as the sum of all 10 individual composite symptoms) was summarized by treatment group and analyzed using a linear model with treatment group as a fixed categorical effect. Peak TSS measured from 10 symptoms within the graded symptom scoring system collected 3 times daily was reported. Per protocol, only Molnupiravir PEP and Placebo were presented for this endpoint.

Time frame: From Day 1 AM up to Day 8 post viral inoculation

Part 2: Duration of Grade ≥2 Symptoms From Day 1 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from Grade 0 ("no symptoms") to Grade 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from Grade 0 ("no symptoms") to Grade 4 ("symptoms at rest"). Duration of Grade 2 symptoms is defined as the duration in days from the first occurrence of a Grade 2 or higher symptom until the first 24 hours period where no Grade 2 or higher symptoms are recorded. Per protocol, Molnupiravir PEP and Placebo were included in the analysis.

Time frame: From Day 1 AM up to Day 8 post viral inoculation

Part 2: Time to Symptom Resolution From Day 1 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. Time in days to symptom resolution was defined as the time in days from the beginning of the specified time frame until the beginning of a 24-hour period with no symptoms above the baseline maximum TSS, as measured by graded symptom scoring system collected 3 times daily. Baseline maximum is defined as the maximum TSS on Day -1 (1 day prior to intranasal inoculation). Per protocol, only Molnupiravir PEP and Placebo are reported.

Time frame: From Day 1 AM up to Day 8 post viral inoculation

Part 2: Time to Peak TSS From Day 1 AM Through Day 8 AM After Intranasal Inoculation (Molnupiravir PEP and Placebo)

Participants used a symptom diary card to record the daily severity of 10 clinical symptoms on a scale ranging from 0 ("no symptoms") to 3 ("bothersome and interferes with activities"), with the exception of "shortness of breath" symptom which was scored from 0 ("no symptoms") to 4 ("symptoms at rest"). For each participant, the sum of grade values for each symptom is used to obtain TSS. TSS ranged from 0 to 31, with higher scores indicating greater symptom severity. Time in days to peak TSS was defined as the time from baseline to the time of peak TSS measured by the graded symptom scoring system collected 3 times daily. Per protocol, only Molnupiravir PEP and Placebo are reported.

Time frame: From Day 1 AM up to Day 8 post viral inoculation

Part 2: Number of Participants With One or More AE (Molnupiravir Tx and Molnupiravir PEP)

An AE is 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. The number of participants with one or more AEs are presented. Per protocol, only Molnupiravir PEP and Molnupiravir Tx are reported.

Time frame: Up to approximately 31 days

Part 2: Number of Participants Discontinuing Study Treatment Due to an AE (Molnupiravir Tx and Molnupiravir PEP)

An AE is defined as any untoward medical occurrence in a participant administered a pharmaceutical product temporally associated with the use of study treatment, whether or not considered related to the study treatment. The number of participants who discontinued study treatment due to an AE are presented. Per protocol, only Molnupiravir PEP and Molnupiravir Tx are reported.

Time frame: Up to day 6

Number of Participants With One or More Viral Challenge-Related AE

An AE is defined as any untoward medical occurrence in a participant administered a pharmaceutical product temporally associated with the use of study treatment, whether or not considered related to the study treatment. An AE is viral challenge-related as determined by investigator. The number of participants with one or more viral challenge-related AEs are presented.

Time frame: Up to approximately 31 days

Part 2: Number of Participants With Concomitant Medication Use From Viral Challenge Through Day 28

Concomitant medications were defined as any prescription medications, over the counter drugs or dietary supplements that a participant happened to be taking while on study, in addition to molnupiravir. The number of participants who use at least 1 concomitant medication from viral challenge (Day 0) through Day 28 were reported. Per protocol, only Molnupiravir PEP, Molnupiravir Tx, OTV Tx and Placebo were reported.

Time frame: From Day 0 up to Day 28

Maximum Plasma Concentration (Cmax) of N-hydroxycytidine (NHC)

NHC is the pharmacologically active moiety of molnupiravir (MK-4482) and therefore its primary pharmacokinetic measure. Cmax was defined as the peak concentration of NHC over the dosing interval. Plasma samples were collected at multiple time points pre-and post-administration and used to determine Cmax following oral administration of Molnupiravir. Per protocol, Cmax for only Molnupiravir PEP and Molnupiravir Tx were reported.

Time frame: Day (D) 0, D2, D4: predose D5: predose, 0.5, 1.5, 4, 8, 12, 24, 48, 72 hours post dose

Time to Maximum Plasma Concentration (Tmax) of NHC

NHC is the pharmacologically active moiety of molnupiravir (MK-4482) and therefore its primary pharmacokinetic measure. Tmax was defined as the time to peak concentration. Plasma samples were collected at multiple time points pre-and post-administration and used to determine Tmax following oral administration of Molnupiravir. Per protocol, Tmax for only Molnupiravir PEP and Molnupiravir Tx were reported.

Time frame: Day (D) 0, D2, D4: predose D5: predose, 0.5, 1.5, 4, 8, 12, 24, 48, 72 hours post dose

Area Under the Plasma Concentration From 0 to 12 Hours Postdose (AUC0-12) of NHC

NHC is the pharmacologically active moiety of molnupiravir (MK-4482) and therefore its primary pharmacokinetic measure. Plasma samples were collected at multiple time points pre-and post-administration and used to determine the area under the plasma concentration curve from time 0 to 12 hours (AUC0-12) following oral administration of Molnupiravir. Per protocol, AUC0-12 for only Molnupiravir PEP and Molnupiravir Tx were reported.

Time frame: Day (D) 0, D2, D4: predose D5: predose, 0.5, 1.5, 4, 8, 12 hours post dose

Area Under the Plasma Concentration From Dosing to Last Measurable Concentration (AUC0-Last) of NHC

NHC is the pharmacologically active moiety of molnupiravir (MK-4482) and therefore its primary pharmacokinetic measure. AUC0-last is a measure of total exposure to Molnupiravir in plasma from the start of dosing to the time of the last quantifiable (\<LLOQ\]) sample. Per protocol, AUC0-Last for only Molnupiravir PEP and Molnupiravir Tx were reported.

Time frame: Day (D) 0, D2, D4: predose D5: predose, 0.5, 1.5, 4, 8, 12, 24, 48, 72 hours post dose

Ctrough of NHC

NHC is the pharmacologically active moiety of molnupiravir (MK-4482) and therefore its primary pharmacokinetic measure. The trough concentration (Ctrough) was defined as the lowest concentration before the next dose. Plasma samples were collected at multiple time points pre-and post-administration and used to determine Ctrough. Per protocol, Ctrough for only Molnupiravir PEP and Molnupiravir Tx were reported.

Time frame: Day (D) 0, D2, D4: predose D5: predose, 0.5, 1.5, 4, 8, 12, 24, 48, 72 hours post dose

t1/2 of NHC

NHC is the pharmacologically active moiety of molnupiravir (MK-4482) and therefore its primary pharmacokinetic measure. t1/2 is the amount of time required to clear 50% of NHC following the oral administration of Molnupiravir. Per protocol, t1/2 for only Molnupiravir PEP and Molnupiravir Tx were reported.

Time frame: Day (D) 0, D2, D4: predose D5: predose, 0.5, 1.5, 4, 8, 12, 24, 48, 72 hours post dose