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Shionogi’s oral antiviral for respiratory syncytial virus (RSV) has met its primary endpoint in a Phase II study that saw some participants achieving an 88.94% reduction in viral load.
The Japanese pharmaceutical’s candidate, S-337395, saw success in reducing the impact of the virus as part of a Phase II human challenge study, a type of trial that requires participants to be infected with RSV.
The primary endpoint of the randomised, double-blind trial sought to establish the safety and efficacy of the oral antiviral via the area under the curve (AUC) of the viral load over time. AUC is defined as a summary of the overall viral burden experienced by a patient over a certain period with a higher AUC implying a more intense infection.
The trial involved 114 healthy adults who were actively inoculated with RSV and then administered either S-337395 or placebo for five days.
The S-337395 treatment group showed a statistically significant reduction in viral load, meeting the trial’s primary endpoint. In the highest dose, there was an 88.94% reduction in viral load and a statistically significant improvement in clinical symptom scores.
S-337395 was generally well tolerated, with no serious or severe adverse events nor no dose-dependent increase in incidence or severity of adverse events (AEs).
Shionogi described how S-337395 acts on the viral L protein, which is essential for virus replication. It also follows after the company was granted fast track designation from the US Food and Drug Administration (FDA) in October 2024. The drug is being developed as part of a partnership with the UBE Corporation.
Typically, the symptoms of RSV are similar to those of the common cold but can advance to pneumonia if left untreated. Research conducted by the US Centres for Disease Control estimates that the infection leads to approximately 100,000–150,000 hospitalisations among adults a year.
The virus is very dangerous in infants with research carried out by pharma giant Pfizer in Japan finding that of 8,509 patients aged under two years identified with the infection, 25% of those would go on to require some form of hospitalisation. The same study found that 40% of all RSV‐associated hospitalisations among children impacted those under two years old.
Market research by GlobalData estimates that by 2030 the market for RSV prophylactic products is set to $16bn, up from a value of $582m by the end of 2020.
Commenting on the rapid expansion in the space, Anaelle Tannen infectious disease analyst for GlobalData, said: “In 2020, the only product marketed for RSV prophylaxis was AstraZeneca/AbbVie's Synagis (palivizumab), a mAb only used in high-risk infants. However, the prophylactic landscape will see heavy diversification over the 2020–2030 forecast period with the launch of multiple novel products.