This is a summary, written by members of the CITF Secretariat, of:

Duong S, Burtniak J, Gretchen A, Mai A, Klassen P, Wei Y, Loeppky C, Shaw SY, Bullard J, Caeseele PV, Stein DR. Riding high: seroprevalence of SARS-CoV-2 after 4 pandemic waves in Manitoba, Canada, April 2020–February 2022. BMC Public Health. 2023 December 5; doi: https://doi.org/10.1186/s12889-023-17239-6.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A CITF-funded study, published in BMC Public Health, aimed to obtain a more accurate estimate of the true infection burden of SARS-CoV-2 in the province of Manitoba by accounting for all age groups, vaccination status, and waning antibody levels. The researchers found that ~60% of Manitobans had generated infection-acquired SARS-CoV-2 antibodies by February 2022. The highest levels found in the province were in the Northern and Southern regional health authorities. Of all age groups, children ages 1-9 showed the highest seroprevalence due to infection at 94% while people over 60 had the lowest at 30%. The research was led by Dr. Derek Riley Stein (University of Manitoba) and Scotty Duong (undergraduate medical student, University of Manitoba).

The researchers recruited and tested 14,901 participants for anti-SARS-CoV-2 nucleocapsid and spike IgG antibodies from April 1, 2020, to February 28, 2022. Participant age groups included ages 0-9, 10-19, 20-39, 40-59, and 60+. Basic demographic information including sex, age, regional health authority, postal code, and vaccination status were recorded for epidemiological analysis.

Key findings:

After four waves of the pandemic in Manitoba, the study found:

  • Approximately 60%, or 3 in 5 Manitobans, had generated SARS-CoV-2 antibodies due to infection;
  • Analyses revealed considerable geographical differences in prevalence throughout the province with the Northern Health Region achieving the highest prevalence due to natural infection at 86.9%, with the Southern Region at 71.8% and the Winnipeg Region, home to 70% of Manitoba’s population, at 57.8%;
  • While seroprevalence increased overall, children aged 1-9 had the highest cumulative prevalence at ~94% and adults aged 60+ had the lowest at ~30%.
  • When adjusted for high infection prevalence, the Manitoba infection fatality ratio was similar to the national average;
  • By February 2022, following the roll-out of mass vaccination in the province during 2021, an estimated 93.4% of Manitobans had acquired antibodies to SARS-CoV-2 due to infection or vaccination.

Cadham Provincial Laboratory, the only public health laboratory in Manitoba and where testing was done, receives only limited samples from school-aged children so that age category may have shown higher positive rates in this study.

The very high antibody prevalence post-Omicron may make it harder to utilize the study to inform public policy. However, by capturing quantitative data on waning antibody levels, the study can help inform targeted vaccination strategies to prevent future outbreaks.