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.

Study Overview

• Status: Terminated
• Conditions: Respiratory Syncytial Virus Infection
• Intervention / Treatment: Drug: Sisunatovir; Drug: Placebo

• Study Type: Interventional
• Enrollment (Actual): 16
• Phase: Phase 2; Phase 3

Contacts and Locations

Study Locations

• China
  • Shanghai, China, 201100
    • Shanghai Minhang District Central Hospital
• India
  • Rajasthan
    • Jaipur, Rajasthan, India, 302039
      • Maharaja Agrasen Superspeciality Hospital
• Japan
  • Kanagawa
    • Kawasaki-Shi, Kanagawa, Japan, 210-0852
      • Koukankai Koukan Clinic
  • Kyoto
    • Jōyō, Kyoto, Japan, 610-0113
      • National Hospital Organization Minami Kyoto Hospital
  • Okinawa
    • Shimajiri, Okinawa, Japan, 901-0493
      • Nanbu Tokushukai Hospital
• United States
  • California
    • Garden Grove, California, United States, 92844
      • National Institute of Clinical Research
    • Westminster, California, United States, 92683
      • National Institute of Clinical Research
  • Florida
    • Miami, Florida, United States, 33184
      • De La Cruz Research Center, LLC
    • Mt. Dora, Florida, United States, 32757
      • Adult Medicine of Lake County
    • Mt. Dora, Florida, United States, 32757
      • Adult Medicine of Lake County, Inc.
  • Illinois
    • Oak Lawn, Illinois, United States, 60453
      • Accellacare - DuPage
  • Montana
    • Butte, Montana, United States, 59701
      • Mercury Street Medical Group, PLLC
  • New York
    • Brooklyn, New York, United States, 11220
      • DM Clinical Research - AOM
    • The Bronx, New York, United States, 10455
      • CHEAR Center LLC
  • Pennsylvania
    • Pittsburgh, Pennsylvania, United States, 15236
      • Preferred Primary Care Physicians, Preferred Clinical Research (Ofc 18)
  • Texas
    • Dallas, Texas, United States, 75230
      • Zenos Clinical Research
    • Houston, Texas, United States, 77043
      • Biopharma Informatic, LLC
    • Mesquite, Texas, United States, 75149
      • SMS Clinical Research
    • Mesquite, Texas, United States, 75149
      • Salma Mazhar, MD PA

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

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.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Quadruple

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Placebo Comparator: Placebo	Drug: Placebo; Participants will receive matching placebo tablets from Day 1 to Day 5
Experimental: Sisunatovir	Drug: Sisunatovir; Participants will receive tablets from Day 1 to Day 5

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Number of Participants With Respiratory Syncytial Virus (RSV) Related Hospitalization or Death From Any Cause Through Day 28	RSV related hospitalization included a specialized acute medical care unit within an assisted living facility or nursing home.	From Day 1 (start of study intervention) up to Day 28

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Number of Participants With RSV-Related Visits (Urgent Care/ Emergency Department (ED)/Hospital) or Death From Any Cause Through Day 28	Participants with RSV related visits in a hospital/urgent care or ED requiring no minimum duration of hospitalization were reported in this outcome measure. Investigators determined if a medical visit was related to RSV. RSV-related medical visits were those attendances that would not otherwise occur in the absence of the RSV infection. These may have included: deterioration or decompensation of the lung function that required supplemental oxygen; development of secondary respiratory tract infections that required antibiotic treatment; management of severe symptoms associated with RSV such as fever; worsening or decompensation of cardiac or renal function in participants with underlying cardiac or renal disease.	From Day 1 (start of study intervention) up to Day 28
Number of Participants With Progression of Lower Respiratory Tract Infection (LRTI) Through Day 10	Progression of LRTI was defined as development of LRTI or transition from non-severe LRTI-RSV at randomization to severe LRTI-RSV at any time up to and including Day 10. LRTI was defined as: >= 2 lower respiratory signs or symptoms for at least 24 hours including at least 1 lower respiratory sign; or 3 lower respiratory symptoms for at least 24 hours. Lower respiratory symptoms included following: new or increased sputum, new or increased cough, new or increased dyspnea (shortness of breath). Lower respiratory signs included: new or increased wheezing, new or increased crackles/ronchi based on chest auscultation, respiratory rate >= 20 respirations/minute, low or decreased oxygen saturation (O2 less than (<) 95 percent (%) or <= 90% if pre-season baseline is < 95%), need for new or increased oxygen supplementation.	From randomization on Day 1 up to Day 10
Number of Participants With Development of LRTI Through Day 10	Development of LRTI was defined as transitioning from not having LRTI at randomization but having nsLRTI-RSV or sLRTI-RSV at any time up to and including Day 10. LRTI was defined as: >= 2 lower respiratory signs or symptoms for at least 24 hours including at least 1 lower respiratory sign; or 3 lower respiratory symptoms for at least 24 hours. Lower respiratory symptoms included following: new or increased sputum, new or increased cough, new or increased dyspnea (shortness of breath). Lower respiratory signs included: new or increased wheezing, new or increased crackles/ronchi based on chest auscultation, respiratory rate >= 20 respirations/minute, low or decreased oxygen saturation (O2 < 95 % or <= 90% if pre-season baseline is < 95%), need for new or increased oxygen supplementation.	From randomization on Day 1 up to Day 10
Number of Participants With Resolution of LRTI at Day 15	Resolution of LRTI was defined as transition from RSV-related non-severe LRTI (nsLRTI-RSV) or RSV-related severe LRTI (sLRTI-RSV) at randomization to not having nsLRTI and sLRTI-RSV. LRTI was defined as: >= 2 lower respiratory signs or symptoms for at least 24 hours including at least 1 lower respiratory sign; or 3 lower respiratory symptoms for at least 24 hours. Lower respiratory symptoms included following: new or increased sputum, new or increased cough, new or increased dyspnea (shortness of breath). Lower respiratory signs included: new or increased wheezing, new or increased crackles/ronchi based on chest auscultation, respiratory rate >= 20 respirations/minute, low or decreased oxygen saturation (O2 < 95 % or <= 90% if pre-season baseline is < 95%), need for new or increased oxygen supplementation.	Day 15
Mean Number of Hospital Free Days Through Day 28		From Day 1 (start of study intervention) up to Day 28
Number of Participants With Progression of LRTI Through Days 3, 5, 15 and 28	Progression of LRTI was defined as development of LRTI or transition from non severe LRTI-RSV at randomization to severe LRTI-RSV at any time up to and including Days 3, 5, 15 and 28. LRTI was defined as: >= 2 lower respiratory signs or symptoms for at least 24 hours including at least 1 lower respiratory sign; or 3 lower respiratory symptoms for at least 24 hours. Lower respiratory symptoms included following: new or increased sputum, new or increased cough, new or increased dyspnea (shortness of breath). Lower respiratory signs included: new or increased wheezing, new or increased crackles/ronchi based on chest auscultation, respiratory rate >= 20 respirations/minute, low or decreased oxygen saturation (O2 < 95 % or <= 90% if pre-season baseline is < 95%), need for new or increased oxygen supplementation.	From randomization on Day 1 up to Days 3, 5, 15 and 28
Number of Participants With Development of LRTI Through Days 3, 5, 15 and 28	Development of LRTI was defined as transitioning from not having LRTI at randomization but having nsLRTI-RSV or sLRTI-RSV at any time up to and including Days 3, 5, 15 and 28. LRTI was defined as: >= 2 lower respiratory signs or symptoms for at least 24 hours including at least 1 lower respiratory sign; or 3 lower respiratory symptoms for at least 24 hours. Lower respiratory symptoms included following: new or increased sputum, new or increased cough, new or increased dyspnea (shortness of breath). Lower respiratory signs included: new or increased wheezing, new or increased crackles/ronchi based on chest auscultation, respiratory rate >= 20 respirations/minute, low or decreased oxygen saturation (O2 < 95 % or <= 90% if pre-season baseline is < 95%), need for new or increased oxygen supplementation.	From randomization on Day 1 up to Days 3, 5, 15 and 28
Number of Participants With Resolution of LRTI at Days 3, 5, 10 and 28	Resolution of LRTI was defined as transition from nsLRTI-RSV or sLRTI-RSV at randomization to not having nsLRTI and sLRTI-RSV. LRTI was defined as >= 2 lower respiratory signs or symptoms for at least 24 hours including at least 1 lower respiratory sign; or 3 lower respiratory symptoms for at least 24 hours. Lower respiratory symptoms included following: new or increased sputum, new or increased cough, new or increased dyspnea (shortness of breath). Lower respiratory signs included: new or increased wheezing, new or increased crackles/ronchi based on chest auscultation, respiratory rate >= 20 respirations/minute, low or decreased oxygen saturation (O2 < 95% or <= 90% if pre-season baseline is < 95%), need for new or increased oxygen supplementation.	At Days 3, 5, 10 and 28
Number of Participants With Improvement of LRTI at Days 3, 5, 10, 15 and 28	Improvement in LRTI status was defined as LRTI resolution or transition from sLRTI-RSV at randomization to nsLRTI-RSV. LRTI was defined as: >= 2 lower respiratory signs or symptoms for at least 24 hours including at least 1 lower respiratory sign; or 3 lower respiratory symptoms for at least 24 hours. Lower respiratory symptoms included following: new or increased sputum, new or increased cough, new or increased dyspnea (shortness of breath). Lower respiratory signs included: new or increased wheezing, new or increased crackles/ronchi based on chest auscultation, respiratory rate >= 20 respirations/minute, low or decreased oxygen saturation (O2 < 95 % or <= 90% if pre-season baseline is < 95%), need for new or increased oxygen supplementation.	At Days 3, 5, 10, 15 and 28
Mean Number of RSV Related Days in Hospital Through Day 28	RSV related hospitalization included a specialized acute medical care unit within an assisted living facility or nursing home.	From Day 1 (start of study intervention) up to Day 28
Mean Number of RSV Related Days in Intensive Care Unit (ICU) Through Day 28		From Day 1 (start of study intervention) up to Day 28
Number of Participants With a Clinical Response of Improvement or Resolution at Days 5, 10, 15, and 28	Improvement was defined as no new acute respiratory infection (ARI) signs or symptoms, and no worsening of existing signs or symptoms compared to the Day 1 visit. At least one sign or symptom (but not all) present at Day 1 was absent, improved or returned to pre-infection status. Resolution was defined as all ARI signs or symptoms were absent or returned to pre-infection status. Clinical response was evaluated by the investigator.	At Days 5, 10, 15, and 28
Number of Participants With Undetectable RSV Viral Load at Days 3, 5, 10, 15 and 28	Undetectable RSV viral load at a visit was defined as a central PCR laboratory result of target not detected (TND).	At Days 3, 5, 10, 15, and 28
Change From Baseline in Log10 Transformed Total RSV Viral Load at Days 3, 5, 10, 15 and 28	Undetectable viral load was considered to be 0 copies/mL for this analysis.	Baseline (within 1 hour post start of study intervention on Day 1) and Days 3, 5, 10, 15, and 28
Number of Participants With Treatment Emergent Adverse Events (TEAEs) Through Day 35	An AE was any untoward medical occurrence in a clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An adverse event was considered a TEAE if the event started on or after the study intervention start date (Day 1).	From Day 1 of study intervention up to 28-30 days after last dose of study drug (up to Day 35)
Number of Participants With Treatment Emergent Serious Adverse Events (TESAE) Through Day 35	An SAE was defined as any untoward medical occurrence that, at any dose, met one or more of the criteria listed below: resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, was a congenital anomaly/birth defect, suspected transmission via a Pfizer product of an infectious agent, pathogenic or nonpathogenic and other important medical event.	From Day 1 of study intervention up to 28-30 days after last dose of study drug (up to Day 35)
Plasma Concentrations of Sisunatovir at Days 3 and 5		Anytime between 3 to 8 hours post dose on Day 3, and pre-dose on Day 5

Collaborators and Investigators

• Sponsor: Pfizer
• Investigators: Study Director: Pfizer CT.gov Call Center, Pfizer

Publications and helpful links

Helpful Links

• To obtain contact information for a study center near you, click here.

Study record dates

Study Major Dates

• Study Start (Actual): December 8, 2023
• Primary Completion (Actual): September 30, 2024
• Study Completion (Actual): September 30, 2024

Study Registration Dates

• First Submitted: October 6, 2023
• First Submitted That Met QC Criteria: October 6, 2023
• First Posted (Actual): October 12, 2023

Study Record Updates

• Last Update Posted (Actual): November 10, 2025
• Last Update Submitted That Met QC Criteria: October 27, 2025
• Last Verified: October 1, 2025

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Infections; RNA Virus Infections; Virus Diseases; Pneumovirus Infections; Paramyxoviridae Infections; Mononegavirales Infections; Respiratory Syncytial Virus Infections; sisunatovir
• Other Study ID Numbers: C5241007; 2023-505922-32-00 (Registry Identifier: CTIS (EU))

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical_trials/trial_data_and_results/data_requests.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: Yes