The relative effectiveness of three and four doses of COVID-19 vaccine in Victoria, Australia: A data linkage study

Jose T Canevari; Allen C Cheng; Logan Wu; Stacey L Rowe; Dennis E Wollersheim; Daniel West; Suman S Majumdar; Sheena G Sullivan

doi:10.1016/j.vaccine.2023.11.047

The relative effectiveness of three and four doses of COVID-19 vaccine in Victoria, Australia: A data linkage study

Vaccine. 2024 Jan 1;42(1):53-58. doi: 10.1016/j.vaccine.2023.11.047. Epub 2023 Dec 5.

Authors

Jose T Canevari¹, Allen C Cheng², Logan Wu³, Stacey L Rowe⁴, Dennis E Wollersheim⁵, Daniel West⁶, Suman S Majumdar⁷, Sheena G Sullivan⁸

Affiliations

¹ Department of Health, Melbourne, Australia; The University of Melbourne, Melbourne, Australia.
² Monash University, Melbourne, Australia; Monash Health, Melbourne Australia.
³ Department of Health, Melbourne, Australia; Walter and Eliza Hall Institute, Melbourne, Australia; The University of Melbourne, Melbourne, Australia.
⁴ Department of Health, Melbourne, Australia; Monash University, Melbourne, Australia; University of San Francisco, USA.
⁵ Department of Health, Melbourne, Australia; La Trobe University, Melbourne, Australia.
⁶ Department of Health, Melbourne, Australia.
⁷ Department of Health, Melbourne, Australia; Monash University, Melbourne, Australia; Burnet Institute, Melbourne, Australia.
⁸ Department of Health, Melbourne, Australia; WHO Collaborating Centre for Reference and Research on Influenza, Melbourne, Australia; University of California, Los Angeles, USA; The University of Melbourne, Melbourne, Australia. Electronic address: sgsullivan@ucla.edu.

PMID: 38057205
DOI: 10.1016/j.vaccine.2023.11.047

Abstract

Background: The Coronavirus Disease 2019 (COVID-19) pandemic led to extensive vaccination campaigns worldwide, including in Australia. Immunity waning and the emergence of new viral variants pose challenges to the effectiveness of vaccines. Our study aimed to assess the relative effectiveness (rVE) of 3 and 4 compared with 2 doses of COVID-19 vaccine. The study focuses on the Victorian population, a majority of whom had no prior exposure to the virus before vaccination.

Methods: We used routinely collected data for the state of Victoria, Australia, to assess rVE during an Omicron-dominant period, 1 June 2022 to 1 March 2023. Immunisation, notifications, hospitalisations and mortality data for residents aged 65 years and older were linked for analysis. Cox proportional hazard regression was used to estimate the rVE against COVID-19 hospitalisation or death, accounting for key confounders with vaccination as a time-varying covariate.

Results: In 1,070,113 people 65 years or older who had received their second dose, a third and fourth dose of a COVID-19 vaccine significantly reduced the hazard of hospitalisation or death compared to two doses. rVE was highest within two weeks from administration at 40 % (95 % CI: 0 % to 64 %) and 66 % (95 % CI: 60 % to 71 %) for a third and fourth dose, respectively. Additional protection conferred by third and fourth doses waned over time from administration.

Conclusions: Our findings underscore the need for additional vaccine doses and updated vaccine strategies. These findings have implications for public health advice and COVID-19 vaccine strategies. Further research and monitoring of vaccine effectiveness in real-world settings are warranted to inform ongoing pandemic response efforts.

Keywords: Australia; COVID-19; Omicron; SARS-CoV-2; Severe outcomes; Vaccine effectiveness; Waning immunity.

MeSH terms

COVID-19 Vaccines*
COVID-19* / prevention & control
Humans
Immunization
Vaccination
Victoria / epidemiology

Substances

COVID-19 Vaccines