Clinical infectious diseases : an official publication of the Infectious Diseases Society of America
October 1, 2026 · via Europe PMC
Phase 2a Randomized Placebo-Controlled Human Challenge Trial of the Respiratory Syncytial Virus L-Protein Inhibitor S-337395 for Respiratory Syncytial Virus Infection.
Byrne S, Baba T, Kawaguchi N, +6 more, Uehara T.
AI summary — for doctors, generated from the abstract only
In a human challenge study, the oral RSV L-protein inhibitor S-337395 lowered viral load, viral titer and symptoms and was well tolerated.
What was studied
A phase 2a, randomized, double-blind, placebo-controlled proof-of-concept trial in the UK, in which healthy adults aged 18-55 were inoculated with RSV-A and given once-daily S-337395 (four dose groups) or placebo for 5 days after evidence of infection, with viral load measured by qRT-PCR.
Key findings
- 114 participants were randomized and 60 formed the infected efficacy set
- Adjusted viral load AUC by qRT-PCR was significantly lower in the 30-mg and 300-mg groups (64.87% and 88.94% reductions)
- The authors conclude viral titer and symptoms were also significantly reduced, and the drug was well tolerated
Clinical relevance
This supports further development of an oral RSV antiviral, which currently has no widely available treatment option.
Who should care
Limitations
The abstract is truncated before the P values and the remaining results, so viral titer and symptom data are not shown here. It is a challenge model in healthy young adults, not natural infection in high-risk patients, and is a small single-center study.
S-337395 shows antiviral activity in a challenge model, but efficacy in real-world patients still needs testing.
This is an AI-generated summary of the published abstract, not a clinical recommendation. It may not reflect the full text or subsequent updates — verify against the original source before acting on it.
Abstract
Background
S-337395 is a novel inhibitor of the respiratory syncytial virus (RSV) L-protein, and a potential oral antiviral against RSV. This phase 2a, randomized, double-blind, placebo-controlled, single-center, proof-of-concept trial conducted in the United Kingdom (April-October 2024) evaluated the efficacy, safety, and dose-response relationship of S-337395 against RSV infection in a human challenge model.
Methods
Healthy adults aged 18-55 years meeting predefined eligibility criteria were inoculated with RSV-A Memphis 37b on Day 0. Nasal washes were collected for quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) assessment twice daily on Days 2-12 and once on Day 13. Participants were randomized 5:13:13:13:13 to receive S-337395 (1, 10, 30, or 300 mg) or placebo, once daily for 5 days upon evidence of infection. Efficacy analyses were conducted in participants with confirmed RSV infection in intent-to-treat infected (ITT-I) set. Safety was assessed in all randomized participants. Dose-response was evaluated across a wide dose range (1-300 mg).
Results
Of 114 randomized participants, 60 comprised the ITT-I set. Covariate-adjusted mean viral load area under the curve (VL-AUC) was significantly lower in the 30- and 300-mg groups by qRT-PCR (64.87% and 88.94% reductions, respectively, both P < .05) and by viral culture assay (72.32% and 86.17% reductions, respectively, both P < .05). Total symptom score AUC was 78.15% lower in the 300-mg group (P < .05). S-337395 was well-tolerated without any safety concerns.
Conclusions
S-337395 significantly reduced viral load, viral titer, and symptoms, and was well-tolerated in this human challenge study. Clinical Trial Registration: ISRCTN24865912.
DOI
10.1093/cid/ciag367
PMID
42294538
PMCID
PMC13644856
Research metadata (titles, abstracts, authors, publication dates) is sourced from Europe PMC, which aggregates content from PubMed/MEDLINE, PubMed Central, and other providers under the U.S. National Library of Medicine (NLM/NCBI). NLM does not claim copyright on abstracts; the original journal publishers or authors may hold rights to the full articles. AI-generated summaries are derived only from the abstract, never the full text, and are always labeled as AI-generated.
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