A Study to Learn About the Study Medicine Sisunatovir in Adults With Respiratory Syncytial Virus (RSV) Infection

AN INTERVENTIONAL PHASE 2/3, ADAPTIVE, MULTI-CENTER, RANDOMIZED, DOUBLE-BLIND STUDY TO INVESTIGATE EFFICACY AND SAFETY OF ORAL SISUNATOVIR COMPARED WITH PLACEBO IN NON-HOSPITALIZED SYMPTOMATIC ADULTS WITH RESPIRATORY SYNCYTIAL VIRUS INFECTION WHO ARE AT RISK OF PROGRESSION TO SEVERE ILLNESS

The purpose of this study is to learn about the safety and effects of sisunatovir. Sisunatovir is studied for the possible treatment of Respiratory Syncytial Virus (RSV). RSV is a virus that causes lung infections with cold-like symptoms, but it can cause severe illness in some people. Sisunatovir is studied in adults:

• who are not admitted to the hospital and
• who have high chances of having a severe illness from RSV infection.

This study is seeking participants who:

• Are confirmed to have RSV.
• Have symptoms of a lung infection.
• Are 18 years of age or older.
• Have one or more of the following which increases the chances of RSV illness:
• A long-term lung disease.
• heart failure.
• a condition that weakens the immune system.
• Are 65 years of age or older and do not have any of the conditions above

Half of the participants in this study will receive sisunatovir. The other half will receive a placebo for 5 days. Placebo looks same like the study medicine but does not have any medication. Both sisunatovir and placebo will be taken by mouth. The study will compare the experiences of people receiving sisunatovir to those of the people who do not. This will help decide if sisunatovir is safe and effective.

Participants will attend about 8-10 study visits over 5 weeks. During this time, they will have:

• visits at the study clinic,
• blood work,
• swabs of the nose,
• questionnaires,
• a follow-up phone call.

Inclusion Criteria:

• Participants aged 18 years or older at screening.
• Diagnosis of RSV infection collected within 5 days prior to randomization.
• New onset or worsening (if present chronically) of at least one of the following signs and/or symptoms consistent with a viral acute respiratory infection (ARI), within 5 days prior to randomization: nasal congestion, nasal discharge, sore throat, cough, sputum production, shortness of breath, or wheezing.
• Has at least 1 of the following characteristics or underlying medical conditions: a) 65 years of age or older b) Chronic lung disease, c) Heart failure, d) Immunosuppressive disease/condition or immune-weakening medications

Exclusion Criteria:

• Any medical or psychiatric condition that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study or interfere with the evaluation of response to the study intervention.
• Diagnosis of viral respiratory infections other than RSV including influenza and SARS-CoV-2
• Current need for hospitalization or anticipated need for hospitalization for any reason to provide inpatient/acute care within 24 hours after randomization
• Any clinically significant ECG abnormality in the pre-dose ECG that, per investigator judgement, may affect participant safety
• Has hypersensitivity to or other contraindication to any of the components of the study interventions, as determined by the investigator.