A Phase 2 interventional study of S-337395 and Placebo in Respiratory Syncytial Virus Infections, sponsored by Shionogi. Recruiting at 89 sites in 8 countries. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-10-21.
Sponsored by Shionogi · Phase 2, Interventional, and Treatment
The main purpose of this study is to investigate the antiviral effect of S-337395 compared with placebo among nonhospitalized adult participants with high-risk factors for progression to severe RSV infection starting intervention within 72 hours of RSV symptom onset.
306 studies on the registry are indexed under Respiratory Syncytial Virus Infections; 50 are open to participants now.
This study's planned enrollment of 192 is above the median of 89 across 223 interventional studies indexed under Respiratory Syncytial Virus Infections.
Browse Respiratory Syncytial Virus Infections studies →Shionogi is the lead sponsor of 105 studies on the registry; 10 are open to participants now.
Of its 39 completed or terminated interventional studies of FDA-regulated products, 21 (54%) have results posted.
Counted across the registry records on this site, refreshed daily.
Key Inclusion Criteria:
Has at least 1 of the following risk factors for severe RSV disease:
Key Exclusion Criteria:
Note: Other protocol-specified inclusion and exclusion criteria may apply.
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
A recording of the heart’s electrical activity, taken with stickers on the chest, arms and legs. It takes a few minutes and does not hurt.
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.
The other ingredients in a medicine besides the active drug, such as fillers, colours or preservatives.
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
ECG (electrocardiogram)
A recording of the heart’s electrical activity, taken with stickers on the chest, arms and legs. It takes a few minutes and does not hurt.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Immunosuppression
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hypersensitivity
An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Excipients
The other ingredients in a medicine besides the active drug, such as fillers, colours or preservatives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Cancer (malignancy)
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Clinically significant
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Participants will receive a high dose of S-337395 twice daily (BID) orally for up to 5 days.
Drug: S-337395
Participants will receive a low dose of S-337395 BID orally for up to 5 days.
Drug: S-337395
Participants will receive matching placebo BID orally for 5 days.
Drug: Placebo
S-337395 will be administered per schedule specified in the arm description.
Placebo matched to S-337395 will be administered per schedule specified in the arm description.
Change From Baseline in RSV Ribonucleic Acid (RNA) Load by Quantitative Reverse Transcription Polymerase Chain Reaction (qRT-PCR) (Nasopharyngeal Swab) at Day 2
Time frame: Baseline, Day 2
Change From Baseline in RSV RNA Load by qRT-PCR (Nasopharyngeal Swab) at Day 4
Time frame: Baseline, Day 4
Change From Baseline in RSV RNA Load by qRT-PCR (Nasopharyngeal Swab) at Day 6
Time frame: Baseline, Day 6
Number of Participants With Treatment-emergent Adverse Events (TEAEs)
Time frame: Day 1 up to Day 28
Change From Baseline in Severity of RSV Respiratory Symptom Score Based on the Respiratory Infection Intensity and Impact Questionnaire (RiiQ) Respiratory Symptom Subscale (RiiQ-RSS)
Time frame: Baseline up to Day 6
Change From Baseline in Severity of RSV Systemic Symptoms Score Based on the RiiQ Systemic Symptom Subscale (RiiQ-SSS)
Time frame: Baseline up to Day 6
Change From Baseline in Severity of RSV Total Symptoms Score Based on the Combined RiiQ RSS and RiiQ-SSS
Time frame: Baseline up to Day 6
Time to First Resolution of All Respiratory RSV-related Symptoms Based on the RiiQ-RSS
Time frame: Baseline up to Day 6
Time to Sustained (2 Consecutive Days) Resolution of All Respiratory RSV-related Symptoms Based on the RiiQ-RSS
Time frame: Baseline up to Day 6
Time to First Resolution of All Systemic RSV-related Symptoms Based on the RiiQ-SSS
Time frame: Baseline up to Day 6
Time to Sustained Resolution of All Systemic RSV-related Symptoms Based on the RiiQ-SSS
Time frame: Baseline up to Day 6
Time to First Resolution of All Respiratory and Systemic RSV-related Symptoms Based on the Combined RiiQ RSS and RiiQ-SSS
Time frame: Baseline up to Day 6
Time to Sustained Resolution of All Respiratory and Systemic RSV-related Symptoms Based on the Combined RiiQ RSS and RiiQ-SSS
Time frame: Baseline up to Day 6
Time to First Resolution of Each Separate RSV-related Symptom Based on the RiiQ Symptom Subscale
Time frame: Baseline up to Day 6
Time to Sustained Resolution of Each Separate RSV-related Symptom Based on the RiiQ Symptom Subscale
Time frame: Baseline up to Day 6
Change From Baseline in RSV RNA Load
Time frame: Baseline up to Day 6
Area Under the Curve (AUC) of Change From Baseline in RSV RNA Load
Time frame: Baseline up to Day 6
Time to the First Negative RSV RNA Load by qRT-PCR
Time frame: Baseline up to Day 6
Time to Sustained Negative RSV RNA Load by qRT-PCR
Time frame: Baseline up to Day 6
Percentage of Participants With Negative RSV RNA Load by qRT-PCR
Time frame: Baseline up to Day 6
Time to the First RSV RNA Load <Lower Limit of Quantitation (LLOQ)
Time frame: Baseline up to Day 6
Time to Sustained RSV RNA Load <LLOQ
Time frame: Baseline up to Day 6
Percentage of Participants With RSV RNA Load <LLOQ
Time frame: Baseline up to Day 6
Change From Baseline in Infectious Titer
Time frame: Baseline up to Day 6
AUC of Change From Baseline in Infectious Titer
Time frame: Baseline up to Day 6
Time to the First Negative RSV Infectious Titer
Time frame: Baseline up to Day 6
Time to Sustained Negative RSV Infectious Titer
Time frame: Baseline up to Day 6
Percentage of Participants With Negative RSV Infectious Titer
Time frame: Baseline up to Day 6
Time to the First RSV Infectious Titer <LLOQ
Time frame: Baseline up to Day 6
Time to Sustained RSV Infectious Titer <LLOQ
Time frame: Baseline up to Day 6
Percentage of Participants With RSV Infectious Titer <LLOQ
Time frame: Baseline up to Day 6
Plasma Concentration of S-337395 After Repeated Oral Doses of S-337395
Time frame: Baseline up to Day 6
Plasma Concentration of S-337395 12 and 24 Hours After the First Dose and the Last Dose (C12 and C24)
Time frame: 12 hours and 24 hours after first dose (Day 2) and last dose (Day 6)
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From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
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Respiratory Syncytial Virus Infections →