Ensitrelvir Reduced COVID After Household Exposure

By
Kathryn Wighton
May 27, 2026

Conexiant

Overview

The phase 3 SCORPIO-PEP trial demonstrated that ensitrelvir significantly reduced the incidence of symptomatic Covid-19 among household contacts exposed to SARS-CoV-2. By day 10, only 3% of participants receiving ensitrelvir developed Covid-19 compared to 9% in the placebo group, indicating a 67% relative risk reduction.

Background

Covid-19, caused by SARS-CoV-2, remains a significant public health challenge, particularly in household settings where transmission can occur rapidly. Post-exposure prophylaxis (PEP) strategies are critical for preventing symptomatic infections among exposed individuals. Ensitrelvir, currently approved in Japan for mild-to-moderate Covid-19, shows promise as a PEP option based on recent trial findings.

Data Highlights

Group	Covid-19 Cases by Day 10	Risk Ratio	Relative Risk Reduction
Ensitrelvir	30 of 1,030 (3%)	0.33 (95% CI: 0.22–0.49)	67%
Placebo	91 of 1,011 (9%)

Key Findings

Ensitrelvir reduced symptomatic Covid-19 incidence to 3% compared to 9% in placebo by day 10.
The trial reported a 67% relative risk reduction for Covid-19 with ensitrelvir.
Among participants with risk factors for severe illness, Covid-19 developed in 9 of 382 ensitrelvir recipients versus 37 of 374 placebo recipients.
No Covid-19-related hospitalizations or deaths were reported in either group.
Adverse events were similar between ensitrelvir (15%) and placebo (16%) groups.
Genome sequencing revealed no treatment-emergent variants among placebo recipients.

Clinical Implications

The findings suggest that ensitrelvir may be an effective option for post-exposure prophylaxis in household contacts, potentially reducing the burden of symptomatic Covid-19. Clinicians should consider early initiation of treatment within 72 hours of exposure to maximize efficacy.

Conclusion

Ensitrelvir demonstrates significant efficacy in preventing symptomatic Covid-19 among household contacts, highlighting its potential role in post-exposure prophylaxis strategies. Further studies may be warranted to confirm these findings and explore broader applications.