Older Australians who recently had a COVID-19 booster are significantly less likely to die from the virus compared to unvaccinated people.
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Researchers from the National Centre for Immunisation Research and Surveillance followed 3.8 million Australians, almost every person aged 65 and older, analysing COVID-19-related and other causes of death in 2022.
During this period, Australia went from being a country with no population-based immunity, to one where most people had experienced a COVID infection of the Omicron strain.
Throughout each Omicron wave, researchers found a recent vaccine was highly effective at preventing death in people over 65, but that waned over time.
During the first Omicron wave, vaccine effectiveness peaked at 93 per cent, three months after a third COVID-19 dose for people over 65, and decreased to 63 per cent for those who had a third dose more than six months ago.
During the second Omicron wave, effectiveness was highest, 84 per cent, three months after a fourth dose, and fell to 56 per cent in those that had a dose more than six months before.
Aged care residents - who are at the greatest risk of dying from COVID - were the greatest beneficiaries.
Last winter one virus-related death was prevented for every 157 aged care residents who received a booster, the study showed.
Lead author, Associate Professor Bette Liu, said many previous studies analysed how effective vaccines were at preventing hospitalisation, but few had enough data to examine their ability to prevent death.
"Uniquely, our analysis shows that during each Omicron wave experienced in Australia in 2022, the effectiveness of a COVID-19 vaccine booster against COVID-19 death waned significantly with time in older adults," Prof Liu said.
The analysis was commissioned by the Department of Health and Aged Care as the government gauges how the country responded to the pandemic.
Chief Medical Officer Paul Kelly says the findings validate the government's guidelines.
"These findings confirm that current recommendations for a COVID-19 booster to be given when it has been more than six months since last receipt (or infection) are important to protect older adults against death from COVID-19, particularly for aged care residents,'' he said.
Australian Associated Press
