Abstract
BACKGROUND: Long-term care facilities (LTCFs) remain highly vulnerable to COVID-19. Despite reduced virulence, Omicron's high transmissibility poses ongoing risks. The effect of infection under strict control measures and early antiviral treatment remains unclear. METHODS: We conducted a retrospective cohort study in a 450-bed LTCF, which implemented rigorous infection control and early antiviral use, evaluating survival outcomes during repeated Omicron outbreaks from January 2022 to December 2023 using Cox regression with time-dependent covariates, adjusted for age, sex, comorbidities, and vaccination status. Mortality trends were also compared across three periods: pre-COVID-19 (2018-2019), COVID-19 present in Japan but absent in our facility (2020-2021), and the Omicron outbreak period (2022-2023). RESULTS: Among 623 residents, 253 were infected. Mortality was lower in the infected group than in the uninfected group (16% vs. 26%), and infection was not significantly associated with increased mortality (HR = 1.36; 95% CI: 0.91-2.04; p = 0.14). Although stratified analysis showed higher mortality among infected females, overall mortality during the outbreak period was unexpectedly lower than in prior periods. CONCLUSIONS: In LTCFs with rigorous infection control and early antiviral use, Omicron infection did not raise mortality. Enhanced protocols may have improved survival, even among uninfected residents.