Via medRxiv: Serial cross-sectional estimation of vaccine and infection-induced SARS-CoV-2 sero-prevalence in children and adults, British Columbia, Canada: March 2020 to August 2022. The underestimates of infections are breathtaking. The abstract:
Background
We chronicle SARS-CoV-2 sero-prevalence through eight cross-sectional sero-surveys (snapshots) in the Lower Mainland (Greater Vancouver and Fraser Valley), British Columbia, Canada from March 2020 to August 2022.
Methods
Anonymized-residual sera were obtained from children and adults attending an outpatient laboratory network. Sera were tested with at least three immuno-assays per snapshot to detect spike (S1) and/or nucleocapsid protein (NP) antibodies. Sero-prevalence was defined by dual-assay positivity, including any or infection-induced, the latter requiring S1+NP antibody detection from January 2021 owing to vaccine availability. Infection-induced estimates were used to assess the extent to which surveillance case reports under-estimated infections.
Results
Sero-prevalence was ≤1% by the 3rd snapshot in September 2020 and <5% by January 2021 (4th). Following vaccine roll-out, sero-prevalence increased to >55% by May/June 2021 (5th), ∼80% by September/October 2021 (6th), and >95% by March 2022 (7th). In all age groups, infection-induced sero-prevalence remained <15% through September/October 2021, increasing through subsequent Omicron waves to ∼40% by March 2022 (7th) and ∼60% by July/August 2022 (8th). By August 2022, at least 70-80% of children ≤19 years, 60-70% of adults 20-59 years, but ∼40% of adults ≥60 years had been infected.
Surveillance case reports under-estimated infections by 12-fold between the 6th-7th and 92-fold between the 7th-8th snapshots.
Interpretation
By August 2022, most children and adults had acquired SARS-CoV-2 vaccine and infection exposures, resulting in more robust hybrid immunity. Conversely the elderly, still at greatest risk of severe outcomes, remain largely dependent on vaccine-induced protection alone, and should be prioritized for additional doses.
Competing Interest Statement
DMS is Principal Investigator on grants from the Public Health Agency of Canada and Michael Smith Foundation for Health Research, paid to her institution, in support of this work and has received grants from the Canadian Institutes of Health Research and the BCCDC Foundation for Public Health, also paid to her institution, for other SARS-CoV-2 work. As the Provincial Health Officer with authority under the emergency provisions of the Public Health Act, BH authorized the access to and analysis of the anonymized sera used in this study; the study was separately reviewed and approved by the University of British Columbia Clinical Research Ethics Board. MK received grants/contracts paid to his institution from Roche, Hologic and Siemens. No other authors have conflicts of interest to disclose.
