Emerging SARS-CoV-2 Resistance After Antiviral Treatment.

Importance: Previous studies have identified mutations in SARS-CoV-2 strains that confer resistance to nirmatrelvir, yet how often this resistance arises and its association with posttreatment virologic rebound is not well understood.

Objective: To examine the prevalence of emergent antiviral resistance after nirmatrelvir treatment and its association with virologic rebound.

Design, Setting, And Participants: This cohort study enrolled outpatient adults with acute COVID-19 infection from May 2021 to October 2023.