Severity of COVID-19 among residents in aged care facilities in Victoria, Australia: A retrospective cohort study comparing the Delta and Omicron epidemic periods

Published:January 19, 2023DOI:
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      During the COVID-19 pandemic, no country with widespread community transmission has avoided outbreaks or deaths in Residential Aged Care Facilities (RACFs). As RACFs residents are at high risk of morbidity and mortality from COVID-19, understanding disease severity risk factors is imperative.


      This retrospective cohort study aimed to compare COVID-19 disease severity (hospitalisation and deaths) and associated risk factors among RACF residents in "[blinded for review]", "[blinded for review]", across Delta and Omicron epidemic periods.

      Settings and participants

      Resident case hospitalisation risk (HR) and case fatality risk (CFR) were assessed using "[blinded for review]" RACFs COVID-19 outbreaks data across two epidemic periods; Delta, 994 resident cases linked to 86 outbreaks; and Omicron, 1,882 resident cases linked to 209 outbreaks.


      Adjusting for outbreak-level clustering, age, sex, up-to-date vaccination status and time since last vaccination, the odds of hospitalisation and death were compared using mixed effects logistic regression.


      The HR and CFR was lower during the Omicron period compared to the Delta period ((HR 8.2% vs 24.6%; OR = 0.17, 95% CI 0.11-0.26) and (CFR 11.4% vs 18.7%; OR = 0.40, 95% CI 0.28-0.56)). During both periods; males had higher odds of hospitalisation and odds of death; being up-to-date with vaccination reduced odds of hospitalisation by 40% (excluding non-emergency patient transfers) and odds of death by 43%; and for each month since last vaccination, odds of hospitalisation increased by 9% and odds of death by 16%.

      Conclusions and implications

      This study provides empirical evidence of lower COVID-19 severity among RACF residents in the Omicron period and highlights the importance of up-to-date and timely vaccination to reduce disease severity in this cohort.

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