Ensitrelvir Pill Shows Promise in Preventing COVID-19 After Exposure in Clinical Trial

On May 13, the New England Journal of Medicine published findings from a clinical trial indicating that the oral medication ensitrelvir significantly lowers the risk of contracting COVID-19 after exposure to the SARS-CoV-2 virus. Conducted between June 2023 and mid-September 2024, the study involved nearly 2,400 participants aged 12 and older across the United States, Argentina, Japan, South Africa, and Vietnam, all of whom had a household contact with confirmed COVID-19. Participants were divided into two groups: one received a five-day course of ensitrelvir within 72 hours of symptom onset in the household contact, while the other received a placebo. Within ten days, symptomatic COVID-19 developed in less than 3% of the ensitrelvir group, compared to around 9% in the placebo group. Lab-confirmed cases were 14% in the ensitrelvir group versus 21.5% in the placebo group. Developed by Shionogi, a Japanese pharmaceutical company, ensitrelvir inhibits an enzyme necessary for the virus's replication, akin to Pfizer's Paxlovid, which did not prevent post-exposure illness in a 2024 NEJM trial. Approved in Japan as Xocova for post-exposure protection, ensitrelvir is currently under FDA review in the U.S., with a decision anticipated in June. Experts stress that this drug should complement vaccination efforts rather than replace them.