The drug ensitrelvir, already approved in Japan to treat COVID-19, can help prevent the disease's spread within households, a large international trial we helped design has found.
Frederick G. Hayden, MD, an emeritus professor at the School of Medicine, presented the trial's results this week in San Francisco.
Only 2.9% of uninfected trial participants who took ensitrelvir went on to developed confirmed cases of COVID-19. That's compared with 9% of the people who received placebos. That means that the drug reduced the risk of contracting COVID from an infected household member by a whopping 67%.
“This is the first clinical trial of an oral antiviral drug to show significant protection against COVID-19,” Dr. Hayden told me. “In addition to vaccination, post-exposure prophylaxis with timely use of an oral antiviral would be a valuable way to help prevent COVID-19 illness in people who have been exposed, especially people at high risk for severe disease."
More than 2,000 people were enrolled in the international trial Dr. Hayden helped design. Participants started taking either ensitrelvir or placebo -- without knowing which -- within 72 hours of a household member first showing COVID symptoms.
For ensitrelvir to become available in the United States for COVID prevention, it will first have to be approved by the federal Food and Drug Administration. The trial could be an important step in that process.