OBJECTIVES: Nursing home residents received updated monovalent SARS-CoV-2 vaccines to protect them from the most recently emerging SARS-CoV-2 variants. We evaluated the extent and durability of clinical protection following receipt of the first monovalent KP.2 vaccination in nursing home residents. DESIGN: Retrospective cohort study using a target trial emulation design. We conducted a sequential, daily comparison of KP.2 vaccination vs no SARS-CoV-2 vaccination during the study period. Residents who received KP.2 were matched to unvaccinated residents based on index date and propensity scores incorporating demographics, vaccination status, and basic clinical characteristics. SETTING AND PARTICIPANTS: Veterans Affairs nursing home residents in long-term care between September 18, 2024, and October 30, 2024. METHODS: The primary exposure was KP.2 vaccination vs no SARS-CoV-2 vaccine during the study period. The primary outcome was a test-confirmed SARS-CoV-2 infection (with or without symptoms). Secondary outcome was composite outcome of COVID-19 infection-associated hospitalizations within 21 days of infection or death within 30 days of infection. RESULTS: Among eligible residents, a matched cohort of 1711 paired person trials were created (average age 76, 95% male, 28% African American). Vaccine effectiveness against COVID-19 infection was 38% at week 12 (95% CI, 13%-56%) and 4% at week 18 (95% CI, -30 to 29%). Vaccine effectiveness against hospitalization or death was 77% at week 12 (95% CI, 60%-90%) and 53% at week 18 (95% CI, 21%-71%). CONCLUSION AND IMPLICATIONS: Vaccination with the KP.2 updated SARS-CoV-2 vaccine provided significant clinical protection against hospitalization or death among nursing home residents. This protection started to wane within a few months of vaccination, mirroring antibody decline reported in other studies. Our findings support consideration of twice-annual vaccination strategy to optimize protection in this vulnerable population.
Gravenstein et al. (Sat,) studied this question.