Abstract
BACKGROUND: Residents of nursing homes remain an epidemiologically important population for COVID-19 prevention efforts, including vaccination. We aim to understand effectiveness of bivalent vaccination for preventing SARS-CoV-2 infections in this population. METHODS: We used a retrospective cohort of nursing home residents from November 1, 2022, through March 31, 2023, to identify new SARS-CoV-2 infections. A Cox proportional hazards model was used to estimate hazard ratios comparing residents with a bivalent vaccination compared with residents not up to date with vaccination recommendations. Vaccine effectiveness was estimated as (1 - Hazard Ratio) * 100. RESULTS: Among 6,916 residents residing in 76 nursing homes included in our cohort, 3,211 (46%) received a bivalent vaccine 7 or more days prior to censoring. Adjusted vaccine effectiveness against laboratory confirmed SARS-CoV-2 infection comparing receipt of a bivalent vaccine versus not up to date vaccine status was 29% (95% Confidence interval 18% to 39%). Vaccine effectiveness for receipt of a bivalent vaccine against residents who were unvaccinated or vaccinated more than a year prior was 32% (95% CI: 20% to 42%,) and was 25% compared with residents who were vaccinated with a monovalent vaccine in the past 61-365 days (95% CI:10% to 37%). CONCLUSIONS: Bivalent COVID-19 vaccines provided additional protection against SARS-CoV-2 infections in nursing home residents during our study time-period, compared to both no vaccination or vaccination more than a year ago and monovalent vaccination 60 - 365 days prior. Ensuring nursing home residents stay up to date with vaccine recommendations remains a critical tool for COVID-19 prevention efforts.