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

Inclusion Criteria:

• Is in good health based on medical history, physical examination, vital signmeasurements, 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 usuallifestyle and agrees to remain abstinent OR uses contraception unless confirmed tobe azoospermic.

• For participants assigned female sex at birth: is not pregnant or breastfeeding, ANDis either not a person of childbearing potential (POCBP) or is a POCBP AND uses acontraceptive method that is highly effective (low user dependency method, OR a userdependent hormonal method in combination with barrier method), or is abstinent frompenile-vaginal intercourse as their preferred and usual lifestyle, has a negativehighly sensitive pregnancy test, abstains from breastfeeding, and has medical,menstrual, and recent sexual activity history reviewed by the investigator todecrease risk of early undetected pregnancy.

Exclusion Criteria:

• Has a history of, or has currently active, symptoms or signs suggestive of upper orlower 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 timeof prestudy visit, or expected during the conduct of the study, or has a history ofclinically 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 tosevere rhinitis, or history of seasonal allergic rhinitis likely to be active at thetime of inclusion into the study and/or requiring regular nasal corticosteroids onan at least weekly basis, within 30 days prior to admission to quarantine.

• Has a history of atopic dermatitis/eczema which is clinically severe and/orrequiring moderate to large amounts of daily dermal corticosteroids.

• Has a diagnosis of cluster headache/migraine or is receiving prophylaxis againstmigraine.

• Has a lifetime history of anaphylaxis and/or a lifetime history of severe allergicreaction. 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 priorto the prestudy visit.

• Uses or anticipates the use of concomitant medications, including vitamins or herbaland dietary supplements from approximately 2 weeks prior to the planned date ofviral challenge until the poststudy visit.

• Has evidence of receipt of vaccine within the 4 weeks prior to the planned date ofviral 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 ofviral challenge.

• Has received 3 or more investigational drugs within the previous 12 months prior tothe planned date of viral challenge.

• Has had prior inoculation with a virus from the same virus subtype as the challengevirus.

• Has had prior inoculation with a virus from the same virus-family as the challengevirus in the last 12 months.

• Has had prior participation in another human viral challenge study with arespiratory virus in the preceding 3 months, taken from the date of viral challengein 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 beveragesor xanthine-containing products.

• Has any significant abnormality altering the anatomy of the nose in a substantialway 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 abusewithin approximately 1 year.