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Effectiveness of COVID-19 Vaccination Against Covid-19 Specific and All-Cause Mortality in Older Australians
25 Pages Posted: 16 May 2023
More...Abstract
Background: Few studies have examined effectiveness of COVID-19 vaccines against COVID-19 and all-cause mortality across different pandemic periods in 2022.
Methods: We used linked whole-of-population data from the 2021 Australian Census, Australian Immunisation Register, death registrations and other national datasets including migration data. Among 3.8 million adults aged 65+ years and >170,000 aged care residents, we used survival analysis to estimate vaccine effectiveness (VE) against COVID-19 specific mortality and all-cause mortality, by vaccine dose and time since receipt, adjusted for age, sex and other factors. We also estimated absolute COVID-19 mortality rates.
Results: From January-May 2022 (Omicron BA.1/2), 3250 COVID-19 deaths occurred; from June-November (Omicron BA.4/5) 3185 COVID-19 deaths occurred. During January-May, VE of a 3rd COVID-19 vaccine dose within 3 months was 93% (95%CI 93-94%) whilst VE of a 2nd dose >6 months since receipt was 34% (26-42%). During June-November, VE of a 4th COVID-19 vaccine dose within 3 months was 84% (82-86%) whilst VE of a 3rd dose >6 months since receipt was 56% (50-62%). VE estimates for aged care residents were similar, but absolute risk reductions were substantially greater. During June-November 2022, we estimated for every 157 aged care residents boosted with a 4th dose, one COVID-19 death was prevented, this compares to 1458 adults boosted per death prevented in those 65+ years.
Conclusions: COVID-19 vaccination is highly effective against COVID-19 mortality among older adults although effectiveness wanes with time since the last dose. Our findings emphasise the importance of continuing to administer booster doses, particularly to those at highest risk.
Funding: This study was funded by the Australian Commonwealth Government Department of Health and Aged Care.
Declaration of Interest: The study authors have no competing interests to declare.
Keywords: COVID-19, vaccine effectiveness, mortality, waning effectiveness
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