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

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 nursing home residents for the extent and durability of protection from hospitalization or death after monovalent KP.2 vaccination.

DESIGN

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.

SETTING AND

PARTICIPANTS

Long-stay residents living in Veterans Affairs nursing homes 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. Secondary outcome was composite outcome of COVID-19-associated hospitalizations within 21 days or death within 30 days of confirmed 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.