The purpose of this study is to investigate the drug-drug interaction between VX-787 and oseltamivir, when co-administered at steady-state in healthy participants. In addition the safety, tolerability and pharmacokinetics (the study of the way a drug enters and leaves the blood and tissues over time) of VX-787 will be assessed.

This study consists of 2 parts. Part 1 is an open-label (a medical research study in which participants and researchers are told which treatments the participants are receiving), randomized (treatment group assigned by chance), 3-way crossover (a method used to switch participants from one treatment group to another in a clinical trial) study to estimate drug-drug interaction between VX-787 and oseltamivir. It consists of 3 phases: a Screening phase, a Treatment phase and a Follow-up phase. Treatment phase will include 3 treatment sessions, each of the participant will receive Treatment A (VX-787, 600 milligram [mg] 2 times a day on Day 1 to 4, followed by a single dose of VX 787, 600 mg on Day 5); Treatment B (Oseltamivir, 75 mg 2 times a day on Day 1 to 4, followed by a single dose of oseltamivir 75 mg on Day 5) and Treatment C (VX-787, 600 mg 2 times a day + oseltamivir, 75 mg 2 times a day on Day 1 to 4, followed by a single dose of VX-787, 600 mg + a single dose of oseltamivir, 75 mg on Day 5). Each treatment session will be separated by a wash-out period of 5 days. The order each participant will receive treatments A, B and C will be decided at randomization.

Part 2 is double-blind (a medical research study in which neither the researchers nor the participants know what treatment the subjects is receiving), randomized, placebo-controlled. It consists of 3 phases: a Screening phase, a Treatment phase and a Follow-up phase. In Treatment phase participants will be randomly assigned VX-787, 600 mg or placebo 2 times a day, on Day 1 to 9, followed by a single dose of VX-787 600 mg or placebo in the morning on Day 10. Pharmacokinetic parameters will be assessed primarily. Participants' safety will be monitored throughout the study.

Inclusion Criteria:

• Female participants must be of non-childbearing potential: postmenopausal for at least 2 years (amenorrheal for at least 3 years and a serum follicle stimulating hormone [FSH] level greater than [>] 40 international unit per liter [IU/L]), or surgically sterile (have had a total hysterectomy, bilateral oophorectomy, or bilateral tubal ligation/bilateral tubal clips without reversal operation), or otherwise incapable of becoming pregnant
• Participants must be non-smoking or smoking no more than 10 cigarettes, or 2 cigars, or 2 pipes per day for at least 3 months prior to screening
• Participants must have a Body Mass Index (BMI: weight in kg divided by the square of height in meters) of 18.0 to 30.0 kilogram per meter square [kg/m^2]
• Participants must be willing/able to adhere to the prohibitions and restrictions specified in the protocol and study procedures
• Participants must be healthy on the basis of a medical evaluation that reveals the absence of any clinically significant abnormality and includes a physical examination, medical history, vital signs and the results of blood biochemistry, blood coagulation and hematology test and a urinalysis performed at screening

Exclusion Criteria:

• Participants with a past history of heart arrhythmias (for example, extrasystoli, tachycardia at rest), history of risk factors for Torsade de Pointes syndrome (for example, hypokalemia, family history of long QT Syndrome)
• Participants with a history or evidence of use of alcohol, barbiturates, amphetamines, recreational or narcotic drug use within the past 1 year, which in the Investigator's opinion would compromise participant's safety and/or compliance with the study procedures
• Participants with current hepatitis A infection (confirmed by hepatitis A antibody immunoglobulin M [IgM]), or hepatitis B infection (confirmed by hepatitis B surface antigen [HBsAg]), or hepatitis C infection (confirmed by hepatitis C virus [HCV] antibody), or human immunodeficiency virus type 1 (HIV-1) or HIV-2 infection at study screening
• Participants having a positive urine drug test or alcohol breath test at study screening. Urine will be tested for the presence of amphetamines, benzodiazepines, cocaine, cannabinoids, opioids, methadone and barbiturates
• Participants with known allergies, hypersensitivity, or intolerance to VX-787, oseltamivir, or excipients of the drug products used