Longitudinal COVID-19 Vaccination Records and SARS-CoV-2 Infection Among Older Long-Term Care Facility Residents in Okinawa, Japan: A Retrospective Descriptive Study

BackgroundRepeated COVID-19 vaccination is widely used in long-term care facilities, yet SARS-CoV-2 infection and reinfection continue to occur in frail older populations.Resident-level longitudinal data linking vaccination records with first and recurrent infections remain limited in Japanese long-term care settings. Materials and methodsWe conducted a retrospective descriptive study in a 134-bed long-term care facility in Okinawa, Japan.We linked 976 valid, dated vaccination records for 232 residents from June 7, 2021, through January 16, 2026, to 136 infection episodes among 109 residents from May 22, 2023, through April 30, 2025, using de-identified resident identifiers.Because facility occupancy was dynamic and complete admission and discharge dates were unavailable, not all 232 residents were continuously at risk.Recurrent infection was operationally defined as a new symptomatic episode with a new positive antigen test at least 60 days after the preceding episode, following documented recovery and release from isolation.Analyses were descriptive; incidence rates, vaccine effectiveness, and inferential statistics were not estimated. ResultsAmong 232 residents, 157/232 (67.7%) were female.The mean age at first recorded vaccination was 85.5 ± 8.3 years, and the median total number of documented doses was 4 (interquartile range [IQR], 2-7).Linkage was successful for 89 residents with 114 infection episodes; 20 residents with 22 episodes could not be linked.Linked documented infection occurred in 89/232 residents (38.4%; 95% confidence interval [CI], 32.3%-44.8%).Among these 89 residents, 65/89 (73.0%) had one episode, 23/89 (25.8%) had two, and 1/89 (1.1%) had three.Recurrent infection occurred in 24/89 residents (27.0%; 95% CI, 18.8%-37.0%).The median interval from the first to second episode was 364 days (IQR, 289.5-575; range, 286-599).Before first infection, the median number of documented doses was 5 (IQR, 2-6; range, 0-8).Among 84 residents with prior documented vaccination, the median interval from the most recent dose to first infection was 49 days (IQR, 14.5-131; range, 3-488).Eight aggregate hospitalizations were documented during infection surveillance but could not be linked to the vaccination roster; one resident died during hospitalization and seven returned to the facility. ConclusionsLinking longitudinal vaccination and infection records was feasible and demonstrated a continuing burden of infection and reinfection.However, dynamic occupancy and incomplete time-at-risk data precluded incidence, person-time, dose-specific vaccine-effectiveness, or causal analyses.The dose distribution should not be interpreted as evidence that additional vaccination increased infection risk.Long-term care facilities require layered prevention combining vaccination with rapid testing, infection-control measures, and timely clinical management.