--- title: A Pill to Prevent COVID-19 Shows Promise description: Results from a late-stage study on the new drug ensitrelvir are encouraging. canonical: https://time.com/7267886/pill-prevents-covid-19-study/ author: Alice Park article:opinion: false article:content_tier: free article:published_time: 2025-03-14T16:08:04.000Z article:modified_time: 2026-05-11T04:51:34.863Z article:section: Health og:title: A Pill to Prevent COVID-19 Shows Promise og:description: Results from a late-stage study on the new drug ensitrelvir are encouraging. og:url: https://time.com/7267886/pill-prevents-covid-19-study/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt1b151bfb55026bab/6998c4e447fe51125855b845/covid-19-test.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 og:image:width: 2120 og:image:height: 1193 og:image:alt: covid-19-test og:type: article twitter:card: summary_large_image twitter:title: A Pill to Prevent COVID-19 Shows Promise twitter:description: Results from a late-stage study on the new drug ensitrelvir are encouraging. twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt1b151bfb55026bab/6998c4e447fe51125855b845/covid-19-test.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 ---  # A Pill to Prevent COVID-19 Shows Promise > Sponsored content. 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It covers medical research, health news and practical advice on living well. #### Where can I get reliable health news by email? Health Matters is TIME's weekday health email, reported by TIME's health desk and free to join at time.com/newsletters. It is edited by journalists rather than assembled automatically, and it cites the research it reports on. #### Is Health Matters free? Yes. Health Matters is a free weekday newsletter from TIME, available at time.com/newsletters. #### Who reads TIME's Health Matters newsletter? Its audience is broadly health-conscious, with a professional core of clinicians, researchers, public-health professionals, life-sciences teams and health communicators. ### Sources * TIME Newsletters: [time.com/newsletters](/c/time-nl-health-2026q3/newsletters?i=acb13fba-ecc0-4a87-9dda-f8eff6c6703e&cr=time-nl-health-2026q3-v1)  by [Alice Park](https://time.com/author/alice-park/)  ## Alice Park Senior Correspondent Mar 14, 2025 4:08 PM UTC  Directly above view of Rapid SARS COV 2 (Covid-19) antigen test on a pastel background Directly above view of Rapid SARS COV 2 (Covid-19) antigen test on a pastel background Javier Zayas—Getty Images  by [Alice Park](https://time.com/author/alice-park/)  ## Alice Park Senior Correspondent Mar 14, 2025 4:08 PM UTC By now, most people have reached a resigned acceptance when it comes to COVID-19\. We accept that we’re probably going to get infected at some point during respiratory disease season—and that when we do, we’ll feel sick for a couple of days, and then get over it. But what if you could avoid getting COVID-19 altogether? That’s the potential promise of a new study on a drug made by Japanese pharmaceutical company Shionogi. At a scientific conference in San Francisco, researchers [reported](https://www.croiconference.org/preliminary-agenda/) that their drug, ensitrelvir, helped prevent people who were exposed to SARS-CoV-2 from testing positive for the disease. There is currently no drug approved to prevent COVID-19, but ensitrelvir is already approved in Japan as a treatment for COVID-19\. It reduces hospitalizations for COVID-19 among people at the highest risk of complications; for the less vulnerable, it cuts down on the number of days they're sick with symptoms. The U.S. Food and Drug Administration is considering the drug for fast-track approval as a way to prevent COVID-19, based on this latest study presented at the Conference of Retroviruses and Opportunistic Infections. (The study has not yet been published in a peer-reviewed journal.) Researchers studied more than 2,300 people age 12 and older who didn't have COVID-19 but lived with someone who had tested positive at the time of the study. They were then randomly assigned to receive either ensitrelvir or placebo pills for five days. Everyone in the study began taking their pills once a day within three days of when their housemate first reported symptoms of COVID-19.  Ensitrelvir tablets Shionogi Among those who took ensitrelvir, about 3% ended up developing COVID-19, compared to 9% of those taking placebo. It turned out that about 10% of the household members of the person who initially tested positive also were positive, even if they didn't experience symptoms and didn't realize they were positive—which highlights how transmissible the virus can be, and how important it is to protect people from getting the infection. The results mean that the drug lowered the risk of getting COVID-19 by 67%. The idea of using an antiviral treatment to protect people at high risk of infection isn’t new. The popular flu treatment oseltamivir, or Tamiflu, is around [84% effective](https://jamanetwork.com/journals/jama/fullarticle/193547) at protecting people from getting the flu when someone else in their house has it. But when scientists studied antiviral treatments for COVID-19, such as Paxlovid and molnupiravir, they didn’t find the same preventative benefits. **Read More**: [_When Is Tamiflu Worth Taking?_](https://time.com/7210574/when-is-tamiflu-flu-medicine-worth-taking/) “This study is the first where this strategy \[to prevent COVID-19\] was documented to succeed,” says Dr. Frederick Hayden, professor emeritus of medicine at University of Virginia School of Medicine, who presented the data at the conference. Finding a way to prevent COVID-19 is critical, especially for older adults, immunocompromised people, and others who are at high risk of developing complications. In the study, people in this category who were taking the drug reduced their risk of getting COVID-19 by 76%. Avoiding infection also allows people to sidestep complications such as [Long COVID](https://time.com/6835566/what-are-long-covid-symptoms/), for which there aren't yet many treatments. Because ensitrelvir works by blocking the virus’ ability to make more copies of itself, it makes sense that it can both treat and prevent disease, depending on when people take it. The dose for treating COVID-19 is the same as the dose used in the study to prevent disease. If people take ensitrelvir early—within three days of being closely exposed to someone with the virus—then the drug can effectively hamper SARS-CoV-2 enough to prevent it from infecting too many cells. If people take it after they have been infected, the drug can help to reduce the amount of virus the immune system has to manage and can lower the chances of severe disease. “This is really, to my knowledge, the first documentation that one could use an oral antiviral for the prevention of COVID-19 in higher risk transmission settings like households,” says Hayden. ```json [{"@context":"https://schema.org","@type":"NewsArticle","@id":"https://time.com/7267886/pill-prevents-covid-19-study/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/7267886/pill-prevents-covid-19-study/"},"headline":"A Pill to Prevent COVID-19 Shows Promise","datePublished":"2025-03-14T16:08:04.000Z","dateModified":"2026-05-11T04:51:34.863Z","description":"Results from a late-stage study on the new drug ensitrelvir are encouraging.","url":"https://time.com/7267886/pill-prevents-covid-19-study/","keywords":["COVID-19","healthscienceclimate"],"thumbnailUrl":"https://static.time.com/v3/assets/bltea6093859af6183b/blt1b151bfb55026bab/6998c4e447fe51125855b845/covid-19-test.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","author":[{"@type":"Person","name":"Alice Park","jobTitle":"Senior Correspondent","url":"https://time.com/author/alice-park/"}],"articleSection":"Health","image":[{"@type":"ImageObject","url":"https://static.time.com/v3/assets/bltea6093859af6183b/blt1b151bfb55026bab/6998c4e447fe51125855b845/covid-19-test.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","width":1200,"height":675,"headline":"covid-19-test","caption":"covid-19-test","creditText":"Javier Zayas—Getty Images","representativeOfPage":true}],"publisher":{"@type":"Organization","name":"Time","url":"https://time.com/","logo":{"@type":"ImageObject","url":"https://time.com/images/logo.png","width":528,"height":156},"foundingDate":"March 3, 1923","sameAs":["https://www.facebook.com/time","https://www.instagram.com/time/?hl=en","https://twitter.com/time","https://www.pinterest.com/timemagazine"]}},{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/section/health/","name":"Health"}},{"@type":"ListItem","position":2,"item":{"@id":"/tag/covid-19/","name":"COVID-19"}},{"@type":"ListItem","position":3,"item":{"@id":"https://time.com/7267886/pill-prevents-covid-19-study/","name":"A Pill to Prevent COVID-19 Shows Promise"}}]}] ```