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Recent COVID-19 vaccination highly effective against death caused by SARS-CoV-2 infection in older Australians

In Australian adults aged 65 years and older, recent COVID-19 vaccination – a booster dose received in the last three months – reduced the risk of death from SARS-CoV-2 infection by as much as 93 per cent compared to those who were unvaccinated, a new national study of 3.8 million adults has shown. 

The benefit was particularly high for adults resident in aged care facilities, who have significantly higher COVID-19 mortality rates. Between June and November 2022, one COVID-19 death was prevented among aged care residents for every 157 people boosted. 

In this first nationwide population analysis, researchers followed almost all people aged 65 years and older for COVID-19 death and all-cause mortality from death certifications throughout 2022 – a period during which Australia transitioned from being a country with almost no population-based natural immunity to one in which most people had experienced SARS-CoV-2 omicron infection. 

For each wave of SARS-CoV-2 omicron infection, the researchers found that, while a recent vaccine booster was highly effective in preventing death, the effectiveness decreased over time.

Analysis of vaccine recipients during the first omicron wave found vaccine effectiveness against COVID-19 death was highest (93 per cent) in the three months following a third COVID-19 vaccine dose; effectiveness decreased (to 63 per cent) in individuals who had received their third COVID-19 vaccine dose more than six months prior. 

Similarly, during the second omicron wave, vaccine effectiveness against COVID-19 death was highest (84 per cent) in individuals in the three months following a fourth COVID-19 vaccine dose, and effectiveness decreased (to 56 per cent) in those who had received their fourth dose more than six months prior.

The study’s lead author, Associate Professor Bette Liu, from the National Centre for Immunisation Research and Surveillance (NCIRS) and UNSW Sydney, said, “While many studies have described the effectiveness of COVID-19 vaccines against SARS-CoV-2 infection using hospitalisation, few have had sufficient statistical power to examine the outcome of COVID-19 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.” 

Australia’s Chief Medical Officer, Professor Paul Kelly, said, “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.’’

The outcomes of this analysis – which was commissioned and supported by the Australian Government Department of Health and Aged Care to answer important questions about Australia’s response to the COVID-19 pandemic – demonstrate the value of collaboration between the Australian Government and expert researchers.

Associated reading:
This study was highlighted in the Australian Government Data Forum keynote address – delivered by Dr David Gruen AO, Australian Statistician and Head of the APS Data Profession on Wednesday 17 May 2023 – where it was featured as an exciting example of the use of data for public policy.

Media enquiries:

NCIRS media team | | 0429 350 279

Access the study here

Declaration: This study, led by the National Centre for Immunisation Research and Surveillance (NCIRS), in collaboration with the NHMRC Centre of Research Excellence in Medicines Intelligence, UNSW Sydney and the Australian National University, has been published online by Preprints with The Lancet. It has not undergone academic peer review; changes may be made before final publication.

Analyses were conducted as part of the Australian Government Department of Health and Aged Care evaluation of the COVID-19 vaccine program. No individual identifying details were available in the data.