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Ensitrelvir for Covid-19 Postexposure Prophylaxis in Household Contacts
Frederick G Hayden1, Masaharu Shinkai2, Tristan W Clark3
1Division of Infectious Diseases and International Health, Department of Medicine, University of Virginia School of Medicine, Charlottesville.
The New England Journal of Medicine
|May 13, 2026
Summary
Ensitrelvir effectively prevents COVID-19 in household contacts when given within 72 hours of symptom onset. This study shows a significant reduction in infection rates with ensitrelvir compared to placebo for postexposure prophylaxis.
Area of Science:
- Virology
- Infectious Diseases
- Pharmacology
Background:
- Ensitrelvir is an oral protease inhibitor for treating COVID-19.
- No antivirals were previously approved for postexposure prophylaxis in COVID-19 household contacts.
Purpose of the Study:
- To evaluate the efficacy of ensitrelvir for preventing COVID-19 in household contacts.
- To assess ensitrelvir's safety as postexposure prophylaxis.
Main Methods:
- A double-blind, randomized, placebo-controlled trial.
- Participants received ensitrelvir or placebo within 72 hours of index patient's symptom onset.
- Primary endpoint: COVID-19 diagnosis by day 10 (RT-PCR positive and symptoms).
Main Results:
- Ensitrelvir significantly reduced COVID-19 incidence (2.9% vs. 9.0%, RR 0.33, P<0.001).
- Adverse event rates were similar between ensitrelvir and placebo groups (15.1% vs. 15.5%).
- No COVID-19-related hospitalizations or deaths were reported.
Conclusions:
- Ensitrelvir is effective in preventing COVID-19 in household contacts.
- Early administration of ensitrelvir within 72 hours is crucial for prophylaxis.
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