Changing impact of COVID-19 vaccination on COVID-19 mortality in the SARS-CoV-2 omicron variant period, 2022-2025
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Understanding COVID-19 vaccine impact on disease outcome rates is important to inform COVID-19 vaccination program recommendations. Among 4 million Australian adults aged 65+ years we tracked COVID-19 vaccine effectiveness in preventing COVID-19-specific mortality over 7 time-periods between 2022-2025 corresponding to different SARS-CoV-2 Omicron subvariant circulation and variant-specific vaccine formulations. In January-May 2022, ancestral COVID-19 vaccine effectiveness was 93.5% (95%CI 92.6-94.2%); COVID-19 mortality rates in unvaccinated versus recently vaccine boosted individuals (within last 3 months) were 0.93 versus 0.061 per 100 person-years. By December 2024-May 2025, JN.1-variant COVID-19 relative vaccine effectiveness (compared to individuals whose last COVID-19 vaccine was >1 year ago) was 47.7% (95%CI 15.4-67.7%); COVID-19 mortality rates in unvaccinated, vaccinated >1 year ago and JN.1 booster recipients were 0.051, 0.031 and 0.016 per 100 person-years respectively. COVID-19 vaccination significantly reduced COVID-19 mortality in older adults however, the absolute mortality reduction from vaccination is less in 2025 than 2022.
