In their CITF-funded research, in preprint and not yet peer reviewed, Dr. Prabhat Jha and his team leading the Action to Beat Coronavirus (Ab-C) study estimated cumulative seroprevalence of SARS-CoV-2 through infection among unvaccinated adults rose from about 2% after the first wave to 7% after the second. The numbers were based on blood samples from almost 9,000 Canadians in May-September 2020 and from over 7,000 Canadians in January-March 2021.

Key points:

  • Canada’s national infection level of about 2% during the 1st wave rose to about 6-7% during the 2nd wave. The Atlantic provinces exhibited a lower increase (2.8% increase to a seroprevalence of 3.3%) given their ability to uphold tight restrictions from the beginning of the pandemic, creating what they dubbed the “Atlantic Bubble.”
  • Seroprevalence among visible minorities rose sharply from about 2% to over 8% from the 1st to the 2nd wave.
  • Infection fatality rates declined from the first wave (3.7/1000 infections) to the second wave (2.6/1000 infections).
  • A high percentage of people who reported COVID symptoms in the survey were found to have antibodies to SARS-CoV-2.
  • Most infection-induced antibodies persisted for at least seven months.
  • The study took blood samples via self-collected dried blood kits, sent to people’s homes.

Participants were recruited via the Angus Reid Forum, a nationwide panel of Canadian adults aged 18 and older, and were asked to complete an online survey about COVID-19 symptoms. Following the online survey, participants who consented to providing blood samples were sent self-collected dried blood kits in the mail. The authors illustrate the effect of social determinants of health on COVID-19 infection. Self-identifying as a visible minority, a woman, a university graduate, or an Indigenous individual was associated with increases in prevalence and incidence. Further investigation is nevertheless required to better understand this disparity. As well, the authors advocate for a national testing scheme to gain a better understanding of trends over time and across testing assays.

Jha and colleagues suggest that although seroprevalence has increased among Canadians, it remained relatively low even after wave 2, suggesting the need for nearly all adult Canadians to require vaccination to gain immunity and reduce community transmission.

 

Tang X, Sharma A, Pasic M, Brown P, Colwill K, Gelband H, Birnboim HC, Nagelkerke N, Bogoch II, Bansal A, Newcombe L, Slater J, Rodriguez PS, Huang G, Fu SH, Meh C, Wu CN, Kaul R, Langlois MA, Morawski E, Hollander A, Eliopoulos D, Aloi B, Lam T, Abe KT, Rathod B, Fazel-Zarandi M, Wang J, Iskilova M, Pasculescu A, Caldwell L, Barrios-Rodiles M, Mohammed-Ali Z, Vas N, Santhanam DR, Cho ER, Qu K, Jha S, Jha V, Suraweera W, Malhotra V, Mastali K, Wen R, Sinha S, Reid A, Gingras AC, Chakraborty P, Slutsky AS, Jha P. SARS-CoV-2 Seroprevalence During the First and Second Pandemic Waves in Canada. SSRN. 12 Aug 2021. Doi: http://dx.doi.org/10.2139/ssrn.3903944