A pill can stop people from developing COVID after being exposed to the virus, trial finds
Six years after COVID-19 made headlines, an antiviral pill has finally been shown to prevent users from developing the disease after being exposed to the virus.
The drug, called ensitrelvir, was initially approved for use in Japan. as a treatment for COVID-19and it has also been approved as a preventative treatment. Now, promising results from advanced trials have been released as regulators in the United States and Europe consider whether to follow suit, Nature reported.
Ensitrelvir, developed by Japanese pharmaceutical company Shionogi, has been shown to significantly reduce the risk of developing the disease, according to a study published Wednesday (May 13) in The New England Journal of Medicine.
The trial specifically focused on household contact exposures, a common source of spread of SARS-CoV-2. So if your roommate got sick, you could take ensitrelvir in addition to staying away from them at home.
Ensitrelvir works by blocking a key enzyme that the virus relies on to make new copies of itself. This enzyme is also targeted by Paxlovid. But unlike Paxlovid, ensitrelvir was shown to significantly reduce the risk of developing COVID-19 symptoms compared to a placebo in people who had been exposed to the virus.
The newly published trial involved more than 2,000 people who lived with people infected with SARS-CoV-2 between June 2023 and September 2024. About half of the participants received a five-day course of ensitrelvir while the other half received a placebo. Neither the participants nor the researchers knew who received which pill, making the trial “double-blind.”
While 9% of people who received the placebo within 72 hours of exposure developed COVID-19 symptoms, only 2.9% of those who took ensitrelvir became symptomatic.
Trial officials also tested participants for SARS-CoV-2 until the tenth day after exposure: Only 14% of those who received the drug tested positive – with or without symptoms – compared to 21.5% of those who received the placebo.
There was no real difference in side effects between the ensitrelvir and placebo groups; in fact, slightly fewer people in the ensitrelvir group reported adverse events (15.1% versus 15.5%). Reported side effects included temporary, reversible reductions in “good” cholesterol and higher levels of blood fats.
The researchers note that their trial did not take into account factors that might influence the degree of transmission within households, such as household size and whether participants adhere to social distancing. The drug has also not been tested on pregnant women or those taking medications that may interact with the drug.
“This is really the first clear demonstration in a double-blind, placebo-controlled, Phase III trial that we actually have an agent that is easily administered orally and effective if taken in time to protect people exposed to COVID-19 in the household setting,” said the study’s first author. Frederic Haydenprofessor of medicine and pathology at the University of Virginia, said Page Med today.
Beyond households, he said the drug would likely also protect patients in the event of COVID-19 outbreaks in nursing homes and long-term care facilities. It’s just that these uses were not expressly included in the essay.
Ensitrelvir, known by the brand name Xocova, was approved by the Japanese Ministry of Health for the treatment of mild to moderate COVID-19 infections in March 2024 and as a medicine. ways to prevent disease in March 2026. It has also been approved in Singapore.
Shionogi submitted the drug for approval by the United States Food and Drug Administration in September 2025. A decision from the American regulator is expected in June, according to Medpage Today.
This article is for informational purposes only and is not intended to offer medical advice.
Hayden, FG, Shinkai, M., Clark, TW, Luetkemeyer, AF, Sax, PE, Hanage, WP, Gebo, KA, Ikematsu, H., Izumikawa, K., Fukushi, A., Kezbor, S., Sakaguchi, H., Lacey, S., Ichihashi, G., Ohmagari, N., and Uehara, T. (2026). Ensitrelvir for post-exposure prophylaxis to covid-19 in household contacts. New England Journal of Medicine, 394(19), 1905-1915. https://doi.org/10.1056/nejmoa2509306
