A Study to Evaluate the Pharmacokinetics, Safety, and Antiviral Activity of JNJ-63623872 in Combination With Oseltamivir in Adult, and Elderly Hospitalized Participants With Influenza A Infection

A Phase 2, Randomized, Double-blind, Placebo-controlled Study to Evaluate the Pharmacokinetics, Safety, and Antiviral Activity of JNJ-63623872 in Combination With Oseltamivir in Adult and Elderly Hospitalized Patients With Influenza A Infection

The purpose of this study is to evaluate the Pharmacokinetic parameters of JNJ-63623872 in combination with oseltamivir in elderly participants (aged 65 to <= 85 years) compared to adults (aged 18 to <= 64 years) with influenza A infection.

This is a randomized (study medication assigned to participants by chance), double-blind (neither the researchers nor the participants know what treatment the participant is receiving), placebo-controlled, multicenter (when more than one hospital or medical school team work on a medical research study) study to evaluate the effect of JNJ-63623872 in combination with oseltamivir in participants with influenza A infection. The study consists of 3 Phases: Screening visit (1 Day), participants who meet all eligibility criteria will be randomized in a 2:1 ratio to receive study drug in double-blind treatment Phase (7 Days) and follow up Phase (21 Days). The duration of participation in the study for each participant is approximately 28 Days. Primarily Pharmacokinetic parameters of JNJ-63623872 will be measured. Participants' safety will be monitored throughout the study.

Inclusion Criteria:

• Participant requires hospitalization to treat influenza infection and/or to treat complications of influenza infection
• Participant tested positive for influenza A infection within 1 day of signing of the informed consent form (ICF)/assent form using a polymerase chain reaction (PCR)-based rapid molecular diagnostic assay
• Participants must be capable of swallowing study medication tablets and capsules
• Each participant (or their legally acceptable representative) must sign an ICF indicating that he or she understands the purpose of and procedures required for the study and is willing to participate in the study
• Participant must be willing and able to adhere to the prohibitions and restrictions specified in the protocol

Exclusion Criteria:

• Participant received more than 3 doses of the influenza antiviral medication oseltamivir, zanamivir, or peramivir since the start of the influenza symptoms, or ribavirin within 6 months prior to Screening
• Participant is unwilling to undergo regular nasal Mid-turbinate (MT) swabs or has any physical abnormality which limits the ability to collect regular nasal specimens
• Participant is immunocompromised, whether due to underlying medical condition (example, malignancy) or medical therapy (example, medications, chemotherapy, radiation, post-transplant)
• Participant is undergoing peritoneal dialysis, hemodialysis, or hemofiltration
• Participant has an estimated glomerular filtration rate (eGFR) less than or equal to (<=)30 milliliter (mL)/minute (min)/1.73 meter^2 (m^2) according to the Modification of Diet in Renal Disease (MDRD) equation, assessed at Screening or based on the most recent clinically relevant creatinine value if available