Relative effectiveness of COVID-19 vaccination with 3 compared to 2 doses against SARS-CoV-2 B.1.1.529 (Omicron) among an Australian population with low prior rates of SARS-CoV-2 infection. Issue 43 (12th October 2022)

• Record Type: Journal Article
• Authors: Liu, Bette; Gidding, Heather; Stepien, Sandrine; Cretikos, Michelle; Macartney, Kristine
• Is Part Of: Vaccine. Volume 40:Issue 43(2022)
• Page Start: 6288
• Page End: 6294
• Publication Date: 2022-10-12
• Subjects: Vaccines -- Periodicals; 615.372
• DOI: 10.1016/j.vaccine.2022.09.029
• Languages: English
• ISSNs: 0264-410X

Abstract

Highlights: In an infection-naiive population older adult population, recent administration of a 3rd COVID-19 vaccine dose reduced the risk of hospitalisation/death from SARS-CoV-2 Omicron variant by 65% compared to dose 2. Over 6 weeks, one hospitalisation/death was avoided by boosting 192 adults aged 70 + years with a third COVID-19 vaccine dose. Abstract: Background: We estimate effectiveness of 3 versus 2 vaccine doses against SARS-CoV-2 B.1.1.529 Omicron in a mostly infection-naiive but highly vaccinated Australian population. Methods: Cohort study of adults aged 40+ years resident in Sydney followed from 1 January 2022 for SARS-CoV-2 infection and COVID-19 hospitalisation or death using linked immunisation, disease notification and hospitalisation registers. Adjusted hazard ratios (aHR) and corresponding relative vaccine effectiveness (rVE) were estimated comparing 3 to 2 vaccine dose recipients by time since dose receipt, vaccine brand, and prior infection. Absolute risk reductions and numbers needed to boost by age groups were calculated. Results: 2, 053, 123 infection-naiive individuals (mean age 59 years) were followed for 327, 272 person-years for infection and 224, 269 person-years for severe outcomes (hospitalisation/death). There were 175, 849 infections and 4113 hospitalisations/deaths. Compared to individuals receiving dose 2 within the last 3 months, rVE in dose 3 recipients was 7% (95% CI 5–9%) against infection and 65% (95%CI 61–69%) against hospitalisation/death. Almost all dose 3 recipients had an mRNA vaccine; there was little difference in dose 3 rVE by primary course vaccine brand (ChAdOx1 versus BNT162b2). Over the 6-week follow-up, we estimated one hospitalisation/death was avoided for every 192 adults aged ≥70 years boosted with dose 3 in the infection-naiive cohort. The aHR for hospitalisation/death from Omicron was 0.12 (95 %CI 0.07–0.23) for 2-dose recipients with a prior Delta infection compared with 2-dose recipients with no prior infection. Conclusions: Receipt of a third COVID-19 vaccine dose in adults aged 40 years and above significantly reduced hospitalisations and deaths from SARS-CoV-2 Omicron infections in a primarily infection-naiive population.