The oral antiviral drug is proving successful in preventing symptomatic Covid-19 in household members

The oral antiviral drug is proving successful in preventing symptomatic Covid-19 in household members

An international clinical trial has found a drug that may help prevent symptomatic Covid-19 in people exposed in households. The findings could be particularly important for families where someone is at high risk of serious complications from the disease.

The drug, ensitrelvir, is already approved in Japan to treat mild to moderate Covid cases. However, the Scorpio PEP study showed that it also has the potential to protect against disease. Uninfected people who started taking the antiviral within 72 hours of symptoms first appearing in a household member were significantly less likely to contract COVID-19 than people who received an inactive placebo.

Among more than 2,000 trial participants in the U.S. and abroad, 9% of participants who took the developed placebo confirmed cases of Covid-19. This is compared to just 2.9% of people taking ensitrelvir - a 67% reduction in risk of Covid-199 illness.

“In addition to vaccination, post-exposure prophylaxis with timely use of an oral antiviral would be a valuable way to prevent COVID-19 illness in people who have been exposed, particularly those at high risk for severe disease,” said Hayden, MD. (CROI) in San Francisco.

The Scorpio Pep trial, conducted between June 2023 and September 2024, was double-blind, meaning neither the researchers nor the uninfected household participants knew whether they were receiving ensitrelvir or placebo. Household members who took a 5-day course of ensitrelvir after exposure to a proven illness were much less likely to have Covid but no more likely to suffer adverse events than those who took placebo.

Among trial participants, 37% had at least one risk factor for developing serious (and potentially life-threatening) complications. Their risk of developing Covid was significantly reduced, but there were no hospitalizations or deaths in either group.

In summarizing their findings presented today, researchers describe ensitrelvir as effective and generally well tolerated for COVID-19 prevention. Before the drug could be available in the United States, the Federal Food and Drug Administration would have to approve it for that purpose. Hayden and his collaborators say their findings are an essential step in this process.

This is the first clinical trial of an oral antiviral drug to show significant protection against Covid-19. If approved by the Food and Drug Administration for this purpose, it would be an important addition to current preventive strategies. “

Frederick G. Hayden, MD, Division of Infectious Diseases and International Health, UVA School of Medicine

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