Six years after the pandemic began, a new antiviral pill has proven it can prevent COVID-19 after exposure. The drug, ensitrelvir-marketed as Xocova and developed by Japan's Shionogi-was already approved for treatment. Now, late-stage trial results published in The New England Journal of Medicine show it also works as a preventative.
The double-blind, placebo-controlled study enrolled over 2,000 people living with someone infected with SARS-CoV-2. Among those who took ensitrelvir within 72 hours of exposure, only 2.9% developed symptoms, compared to 9% in the placebo group. Additionally, 14% of drug recipients tested positive for the virus within 10 days, versus 21.5% in the placebo group.
Ensitrelvir blocks a key viral enzyme, similar to Paxlovid, but unlike Paxlovid, it showed a clear benefit in preventing symptomatic illness. Side effects were minimal and comparable to placebo, including temporary drops in good cholesterol.
The drug is already approved in Japan and Singapore. Shionogi submitted it for U.S. FDA approval in September 2025, with a decision expected this June.
Beyond households, researchers say it could protect nursing home residents and long-term care facilities during outbreaks.