Durability of Clinical Protection in Nursing Home Residents Following Monovalent KP.2 SARS-CoV-2 Vaccination

Nursing home residents received updated monovalent SARS-CoV-2 vaccines to protect them from the most recently emerging SARS-CoV-2 variants. We evaluated nursing home residents for the extent and durability of protection from hospitalization or death after monovalent KP.2 vaccination.

Retrospective cohort study using a target trial emulation design. We conducted a sequential, daily comparison of those who did and did not receive a KP.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.

Long-stay residents living in Veterans Affairs nursing homes between September 18, 2024, and October 30, 2024.

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. Secondary outcome was composite outcome of COVID-19-associated hospitalizations within 21 days or death within 30 days of confirmed infection.

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%).

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.