Estimating the proportion of Victorians infected with COVID-19 during the Omicron BA.1 epidemic wave of January 2022 in Australia

Authors:

• Altermatt, Aimée
• Heath, Katherine
• Saich, Freya
• Lee Wilkinson, Anna
• Scott, Nick
• Sacks-Davis, Rachel
• Young, Kathryn
• Stoové, Mark
• Gibney, Katherine B.
• Hellard, Margaret

Details:

Australian and New Zealand Journal of Public Health, Volume 47, Issue 1, 2023-02-28

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Objective To estimate the proportion of Victorians infected with COVID-19 in January 2022. Methods Between 11–19 February 2022 we conducted a nested cross-sectional survey on experiences of COVID-19 testing, symptoms, test outcome and barriers to testing during January 2022 in Victoria, Australia. Respondents were participants of the Optimise Study, a prospective cohort of adults considered at increased risk of COVID-19 or the unintended consequences of COVID-19-related interventions. Results Of the 577 participants, 78 (14%) reported testing positive to COVID-19, 240 (42%) did not test in January 2022 and 91 of those who did not test (38%) reported COVID-19-like symptoms. Using two different definitions of symptoms, we calculated symptomatic (27% and 39%) and asymptomatic (4% and 11%) test positivity. We extrapolated these positivity rates to participants who did not test and estimated 19–22% of respondents may have had COVID-19 infection in January 2022. Conclusion The proportion of Victorians infected with COVID-19 in January 2022 was likely considerably higher than officially reported numbers. Implications for public health Our estimate is approximately double the COVID-19 case numbers obtained from official case reporting. This highlights a major limitation of diagnosis data that must be considered when preparing for future waves of infection.