Differential COVID-19 case ascertainment by age and vaccination status in Victoria, Australia: a serosurveillance and record linkage study

Authors

  • Joshua Szanyi Department of Infectious Diseases, University of Melbourne, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia; Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Victoria, Australia
  • David J Price Department of Infectious Diseases, University of Melbourne, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia; Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Victoria, Australia
  • Kylie S Carville Department of Infectious Diseases, University of Melbourne, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia; Victorian Infectious Diseases Reference Laboratory, Royal Melbourne Hospital, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia
  • Mitch Batty Victorian Infectious Diseases Reference Laboratory, Royal Melbourne Hospital, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia
  • Sarah Yallop Victorian Infectious Diseases Reference Laboratory, Royal Melbourne Hospital, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia
  • Suellen Nicholson Victorian Infectious Diseases Reference Laboratory, Royal Melbourne Hospital, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia
  • Theo Karapanagiotidis Victorian Infectious Diseases Reference Laboratory, Royal Melbourne Hospital, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia
  • Stacy Rowe School of Public Health and Preventive Medicine, Monash University, Melbourne, Australia; Department of Health Professions, University of San Francisco, San Francisco, California, US
  • Sheena Sullivan Department of Infectious Diseases, University of Melbourne, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia; Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Victoria, Australia; Victorian Infectious Diseases Reference Laboratory, Royal Melbourne Hospital, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia; Victorian Department of Health, Melbourne, Victoria, Australia
  • Vinay Menon Victorian Department of Health, Melbourne, Victoria, Australia
  • Daniel West Victorian Department of Health, Melbourne, Victoria, Australia
  • Lakshmi Manoharan Victorian Department of Health, Melbourne, Victoria, Australia
  • Eliza Copsey Victorian Department of Health, Melbourne, Victoria, Australia
  • Suman S Majumdar School of Public Health and Preventive Medicine, Monash University, Melbourne, Australia; Victorian Department of Health, Melbourne, Victoria, Australia; Burnet Institute, Melbourne, Victoria, Australia
  • Brett Sutton School of Public Health and Preventive Medicine, Monash University, Melbourne, Australia; Victorian Department of Health, Melbourne, Victoria, Australia
  • Deborah A Williamson Department of Infectious Diseases, University of Melbourne, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia; Victorian Infectious Diseases Reference Laboratory, Royal Melbourne Hospital, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia; Walter and Eliza Hall Institute, Melbourne, Victoria, Australia
  • Jodie McVernon Department of Infectious Diseases, University of Melbourne, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia; Victorian Infectious Diseases Reference Laboratory, Royal Melbourne Hospital, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia; Walter and Eliza Hall Institute, Melbourne, Victoria, Australia

DOI:

https://doi.org/10.33321/cdi.2024.48.28

Keywords:

COVID-19, SARS-CoV-2, serosurveillance, seroprevalence, antibody, vaccination, testing

Abstract

Objectives
To compare serological evidence of prior severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection with linked coronavirus disease 2019 (COVID-19) case notification data in Victoria, Australia, and to determine in vitro SARS-CoV-2 neutralisation activity based on prior infection and vaccination history.
Design, setting, participants
Four cross-sectional serological surveys were conducted between 30 June and 31 October 2022 (a period of Omicron BA.4/BA.5 dominance) using 1,974 residual serum samples obtained from the Victorian Infectious Diseases Reference Laboratory. Serological results were linked to COVID-19 case notification and vaccination data. Surrogate virus neutralisation testing was performed to obtain in vitro inhibition estimates by anti-nucleocapsid serostatus and COVID-19 vaccination history.
Main outcome measures
Adjusted anti-SARS-CoV-2 spike and nucleocapsid seropositivity by sex, age and region of residence; adjusted proportion of cases notified by anti-nucleocapsid serostatus, age and number of COVID-19 vaccination doses received; adjusted percentage in vitro inhibition against wildtype and Omicron BA.4/BA.5 SARS-CoV-2 variants by anti-nucleocapsid serostatus and COVID-19 vaccination history.
Results
The prevalence of anti-SARS-CoV-2 nucleocapsid antibodies was inversely proportional to age. In October 2022, prevalence was 84% (95% confidence interval [95% CI]: 75–93%) among 18–29-year-olds, compared to 39% (95% CI: 27–52%) among ≥ 80-year-olds. In most age groups, approximately 40% of COVID-19 cases appear to have been notified via existing surveillance mechanisms. Case notification was highest among individuals older than 80 years and people who had received COVID-19 vaccine booster doses. In vitro neutralisation of Omicron BA.4/BA.5 sub-variants was highest for individuals with evidence of both prior infection and booster vaccination.
Conclusions
Under-notification of SARS-CoV-2 infections in the Victorian population is not uniform across age and vaccination strata. Seroantibodyprevalence data that give insights into case notification behaviour provide additional context for the interpretation of existing COVID-19 surveillance information.

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Published

21/08/24

How to Cite

Szanyi, Joshua, David J Price, Kylie S Carville, Mitch Batty, Sarah Yallop, Suellen Nicholson, Theo Karapanagiotidis, et al. 2024. “Differential COVID-19 Case Ascertainment by Age and Vaccination Status in Victoria, Australia: A Serosurveillance and Record Linkage Study”. Communicable Diseases Intelligence 48 (August). https://doi.org/10.33321/cdi.2024.48.28.

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Vol. 48 (2024)

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Original article

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