A Study to Investigate the Effects of Sisunatovir on QTc Interval in Healthy Adult Participants.

The purpose of the study is to investigate the effects of multiple oral doses of sisunatovir on QTc Interval. This study is seeking participants who: * are male or female of 18 years of age or older * are examined to be healthy All participants will receive Treatment A, B, and C in a randomized order based on 6 possible sequences. All treatments will be taken by mouth. Participants assigned to treatment A will receive 5 oral doses of sisunatovir administered Q12 hours over 3 days in a fed state. Participants assigned to treatment B will receive 5 oral doses of matching placebo administered Q12 hours over 3 days in a fed state. Participants assigned to treatment C will receive 4 oral doses of placebo administered Q12 hours for 2 days followed by a single dose of 400 mg moxifloxacin on the morning of Day 3. All participants will remain in the study clinic for 4 days for each treatment, for safety review, laboratory collections, and to assess how the study medicine affects QTc intervals. All participants selected in the study will be required to go through a screening period up to 28 days. A screening period is the time during which a few participants are examined to see whether they are fit for the study. During this period, the participant's medical history and past and current medications will be reviewed. A series of tests will also be performed to see if they are good to be selected for the study. If the participant meets all required criteria and are interested in continuing, the participant will be brought into the study clinic to stay overnight for 4 days for each treatment. On day 4, the participant will be discharged. About 28 to 35 days after discharge following the final treatment, the participant will be contacted for a follow up visit either in person or by telephone. This is to check up on how the participant is doing and to conclude the study.