Announcement • May 15

Shionogi & Co., Ltd. Announces Results from Its Global, Double-Blind, Randomized, Placebo-Controlled Phase 3 Study

Shionogi & Co., Ltd. announced that results from its global, double-blind, randomized, placebo-controlled Phase 3 study,SCORPIO-PEP, were published in the New England Journal of Medicine [1]. A five-day course of ensitrelvir significantly reduced the risk of symptomatic COVID-19 by 67% in individuals following exposure to an infected individual through Day 10 compared to placebo.1 Among participants in the primary analysis population (n=2,041) who received ensitrelvir, 2.9% developed symptomatic COVID-19, compared to 9.0% of those who received placebo through Day 10 (risk ratio: 0.33; 95% confidence interval [CI]: 0.22-0.49; pAbout SCORPIO-PEP The global, double-blind, randomized, placebo-controlled Phase 3 study, SCORPIO-PEP, assessed the safety and efficacy of ensitrelvir as post-exposure prophylaxis. The study included 2,387 study participants aged 12 years and older with a negative local screening test for SARS-CoV-2 infection and no symptoms at the time of enrollment, who were exposed to a person living in their household with symptomatic COVID-19. The primary analysis included 2,041 household contact participants with a central laboratory-confirmed negative SARS-CoV-2 test. The trial was conducted from June 2023–September 2024. More than 98% of household contacts tested positive for SARS-CoV-2 N and/or S antibodies, indicating that nearly all had evidence previous SARS-CoV-2 infection or vaccination, or both. Study participants were randomly assigned at a 1:1 ratio to receive ensitrelvir (375 mg on day 1 and 125 mg on days 2-5) or placebo, once daily, and began treatment within 72 hours of when the household member with COVID-19 (index patient) began showing symptoms. Participants then continued ensitrelvir (125 mg) or placebo for five days. SCORPIO-PEP is the first and only Phase 3 study of an oral antiviral to meet the primary endpoint of preventing COVID-19 following exposure to an infected individual. Ensitrelvir is a SARS-CoV-2 main protease inhibitor created through joint research between Hokkaido University and Shionogi. SARS-CoV-2 has an enzyme called the main protease, which is essential for the replication of the virus. Ensitrelvir suppresses the replication of SARS-CoV-2 by selectively inhibiting the main protease. Ensitrelvir is under review by the U.S. FDA for post-exposure prophylaxis (PEP) of COVID-19, with a Prescription Drug User Fee Act (PDUFA) action date of June 16, 2026. Ensitrelvir, known as XOCOVA® in Japan, received emergency regulatory approval [2] in Japan in November 2022 and full approval [3] in March 2024 for the treatment of COVID-19 based on results [4] from SCORPIO-SR, a Phase 3 study conducted in Asia, during the Omicron-dominant phase of the pandemic. Results from this study were published [5] in JAMA Network Open. In 2025, Shionogi submitted a supplemental New Drug Application for COVID-19 treatment in pediatric patients aged 6 to under 12 years in Japan. In March 2026, XOCOVA received approval in Japan for the prevention of COVID-19 following exposure [6]. Ensitrelvir is currently under regulatory review in Taiwan [7] for post-exposure prophylaxis of COVID-19.

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