Following initial serosurveillance activities in 2020, the Australian COVID-19 Serosurveillance Network has embarked on a program of repeat surveys of blood donors. The program aims to estimate the prevalence of antibodies to SARS-CoV-2, whether derived from vaccination or natural infection and examine variations over time using repeat cross-sectional surveys of Australian blood donors. This report describes results from the first survey in this series conducted in late February to early March, approximately 6 weeks past the peak of the Omicron wave in NSW, ACT, Queensland, and Victoria and prior to substantial transmission in Western Australia.
- The prevalence of anti-spike antibodies was very high (98%) across all jurisdictions, with little variation by jurisdiction, age group and sex.
- The prevalence of anti-nucleocapsid antibodies was 17% overall and was highest in Queensland (26%), followed by Victoria (23%) and NSW (21%). Seroprevalence was lowest, at 0.5%, in WA.
- Anti-nucleocapsid seroprevalence was highest among donors aged 18–29 years at 27%, declining with increasing age to 6% in donors aged 70–89 years. These national age-specific patterns were also observed within Victoria, NSW, and Queensland. Seroprevalence was similar for males and females.