Molnupiravir Use and Severe Covid-19 Outcomes During the Omicron Surge

Abstract Background The oral antiviral molnupiravir is moderately effective in high-risk, unvaccinated non-hospitalized patients infected with early variants of SARS-CoV-2. Data regarding the effectiveness of molnupiravir against the B.1.1.529 (omicron) variant and in vaccinated populations are limited. Methods We obtained data for all members of Clalit Health Services, 40 years of age and older, eligible for molnupiravir therapy during the omicron surge. A Cox proportional-hazards regression model with time-dependent covariates was used to estimate the association between molnupiravir treatment and hospitalizations and deaths due to Covid-19, with adjustment for sociodemographic factors, coexisting conditions, and prior Covid-19 immunity status. Results A total of 19,868 participants met the eligibility criteria, of whom 1,069 (5%) received molnupiravir during the study period. In patients 65 years and above, the rate of hospitalizations related to Covid-19 in treated compared to untreated patients was 74.6 versus 127.6 per 100,000 person-days; adjusted hazard ratio (HR) 0.55 (95% CI, 0.34 to 0.88). The adjusted HR for death due to Covid-19 was 0.26 (95% CI, 0.10 to 0.73). Among patients aged 40 to 64, the hospitalizations rate in treated compared to untreated patients was 125.8 versus 49.1 per 100,000 person-days; adjusted HR 1.80 (95% CI, 0.86 to 3.77). The adjusted HR for death was 12.8 (95% CI, 3.41 to 48.2). Conclusions In a cohort of non-hospitalized, omicron-infected high-risk patients, molnupiravir therapy was associated with a significant reduction in hospitalizations and mortality due to Covid-19 in patients 65 years and above. However, no evidence of benefit was found in younger adults.