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S-337395 for high-risk adults with symptomatic RSV

A Phase 2b, Multicenter, Randomized, Double-blind, Placebo-controlled, Parallel-group Study to Evaluate the Safety, Tolerability, and Efficacy of S-337395 in Symptomatic Nonhospitalized Adults With Respiratory Syncytial Virus Who Are at High Risk of Progression to Severe Disease

Phase 2 Interventional Shionogi Inc. · NCT07214571

This trial will test whether taking the antiviral S-337395 within 72 hours of symptoms helps nonhospitalized adults with RSV who are at high risk of progressing to severe illness.

Quick facts

PhasePhase 2
Study typeInterventional
Enrollment192 (estimated)
Ages18 Years and up
SexAll
SponsorShionogi Inc. Industry-sponsored
Drugs / interventionschemotherapy, immunotherapy, radiation
Locations68 sites (Los Angeles, California and 67 other locations)
Trial IDNCT07214571 on ClinicalTrials.gov

What this trial studies

This randomized, placebo-controlled Phase 2 trial gives symptomatic, nonhospitalized adults with PCR-confirmed RSV and at least one high-risk factor either S-337395 or placebo, starting within 72 hours of symptom onset. The primary focus is the antiviral effect of S-337395 compared with placebo, with virologic measures and monitoring for clinical progression or hospitalization. Eligible participants are medically stable aside from RSV and must have risk factors such as age ≥75 years or symptomatic chronic lung or cardiovascular disease requiring ongoing treatment. Safety and tolerability will be followed through exams, ECGs, and adverse event reporting.

Who should consider this trial

Good fit: Nonhospitalized adults with PCR-confirmed symptomatic RSV within 72 hours of symptom onset who are ≥75 years old or have symptomatic chronic lung or cardiovascular disease requiring ongoing treatment.

Not a fit: People who are already hospitalized, who start treatment more than 72 hours after symptom onset, who do not have RSV, or who do not meet the high-risk criteria are unlikely to benefit from this trial.

Why it matters

Potential benefit: If successful, S-337395 could shorten illness, reduce viral levels, and lower the risk of progression to hospitalization in high-risk adults with RSV.

How similar studies have performed: Previous antiviral approaches for RSV have produced mixed results in adults, and S-337395 is a novel candidate that has not yet been proven effective in this population.

Eligibility criteria

Show full inclusion / exclusion criteria 
Key Inclusion Criteria:

* Participants who have new onset or worsening (if present chronically) of at least 1 of the following signs and/or symptoms consistent with a viral acute respiratory infection within 72 hours prior to randomization: fever, nasal congestion, nasal discharge, sore throat, cough, sputum production, shortness of breath, or wheezing.
* Participants diagnosed with RSV infection preferably using a rapid polymerase chain reaction (PCR) or other molecular-based diagnostic assay.
* Has at least 1 of the following risk factors for severe RSV disease:

  1. ≥ 75 years of age;
  2. Chronic lung disease that is symptomatic and requiring chronic treatment; and
  3. Chronic cardiovascular disease that is symptomatic and requiring chronic treatment.
* With the exception of the RSV disease, medically stable on the basis of medical history, physical examination, vital signs, and 12-lead electrocardiogram (ECG) performed at screening.

Key Exclusion Criteria:

* Hospitalized or expected to be hospitalized within 24 hours of screening.
* Is considered by the investigator to be immunocompromised, due to an underlying medical condition or medical therapy, chemotherapy, radiation, stem cell or solid organ transplant.
* Has known allergies, hypersensitivity, or intolerance to S-337395 or to any of the excipients of the S-337395 or placebo formulation.
* Suspicion or known severe renal impairment.
* Any other medical or psychiatric condition making the participant unsuitable for the current study or interfering with the evaluation of response to the study intervention in the opinion of the investigator/subinvestigator.
* Has received a therapy intended to treat RSV infection within 14 days prior to screening.
* Is receiving chemotherapy or immunotherapy for malignancy.
* Has received RSV vaccination within 7 days prior to screening.
* Has had either confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or influenza infection (test was positive) during the 28 days prior to screening.
* Has any other confirmed clinically relevant respiratory infection by any pathogen at, or within 28 days of screening.

Note: Other protocol-specified inclusion and exclusion criteria may apply.

Where this trial is running

Los Angeles, California and 67 other locations

+18 more sites — see ClinicalTrials.gov for the full list.

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
View on ClinicalTrials.gov → Find more trials like this →
Conditions Respiratory Syncytial Virus InfectionsRSV infectionViral infectionS-337395Acute lower respiratory tract infection
Last reviewed 2026-06-15 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.