Observational studyThe Medical journal of Australia2025
Effectiveness of COVID-19 vaccine boosters for reducing COVID-19 mortality among people aged 65 years or older, Australia, August 2023 - February 2024: a retrospective observational cohort study.
Observational study in The Medical journal of Australia, 2025. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
objectivesTo assess the effectiveness of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) monovalent XBB.1.5 variant vaccine for reducing coronavirus disease 2019 (COVID-19) mortality among people aged 65 years or older. STUDY
designRetrospective observational cohort study; analysis of linked 2021 Australian census, Australian Immunisation Register, and death registrations data.
settingAustralia, 1 August 2023 to 29 February 2024; dominant SARS-CoV-2 Omicron subvariants: XBB-related until early December 2023, then the BA.2.86-related JN.1.
participantsPeople aged 65 years or older on 1 August 2023.
main outcome measuresRelative vaccine effectiveness by time since most recent booster and booster type (XBB.1.5 variant or other), adjusted for age, gender, state/territory, household income, number of medical conditions, number of general practice visits, and influenza vaccination during 2022.
resultsBy 29 February 2024, 1620 COVID-19-specific deaths among 4.12 million people aged 65 years or older had been recorded. COVID-19 mortality was lower among people who had received XBB.1.5 COVID-19 booster doses during the preceding 90 days (21 [95% confidence interval {CI}, 9-52] per 100 000 person-years) than among those whose most recent booster had been more than 365 days ago (72 [95% CI, 61-84] per 100 000 person-years). The relative vaccine effectiveness for XBB.1.5 boosters during the preceding 90 days (v any booster > 365 days) was 74.7% (95% CI, 59.9-84.1%); for other booster types it was 51.6% (95% CI, 39.3-61.4%). Relative vaccine effectiveness declined with time: for any booster during the preceding 91-180 days (v any booster > 365 days) it was 31.2% (95% CI, 18.9-41.6%); for any booster during the preceding 181-365 days it was 13.1% (95% CI, 1.8-23.2%). Relative XBB.1.5 vaccine effectiveness was similar in analyses restricted to 1 December 2023 - 29 February 2024, when the dominant Omicron subvariant was JN.1.
conclusionsRecent booster vaccination with the XBB.1.5 monovalent COVID-19 vaccine was highly effective for preventing COVID-19 deaths among people aged 65 years or older, including during the period in which the JN.1 was the dominant SARS-CoV-2 Omicron subvariant. Our findings provide support for the recommendation that people aged 65 years or older receive COVID-19 vaccine booster doses every six months.
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