ABSTRACT
BACKGROUND: Monoclonal antibody (MAB) treatments for COVID-19 received Emergency Use Authorization in the United States. METHODS: We used surveillance data from Rhode Island to conduct a retrospective, statewide cohort study to estimate the effectiveness of MABs for preventing hospitalization and death during periods when Alpha and Delta variants were predominant. RESULTS: From 1/17/2021-10/26/2021, 285 long-term congregate care (LTCC) residents and 3,113 non-congregate patients met our eligibility criteria and received MAB; they were matched to 285 and 6,226 controls, respectively. Among LTCC residents, 8.8% (25/285) of patients who received MAB were hospitalized or died compared to 25.3% (72/285) of those who did not receive MAB (adjusted difference=16.7%, 95% confidence interval CI=11.0-22.3%). Among non-congregate patients, 4.5% (140/3,113) of patients who received MAB were hospitalized or died compared to 11.8% (737/6,226) of those who did not receive MAB (adjusted difference=7.2%, 95% CI=6.0-8.4%). CONCLUSIONS: Administration of MABs led to an absolute reduction in hospitalization or death during periods when Alpha and Delta variants were predominant.