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

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. Assessment of SARS-CoV-2 Seropositivity During the First and Second Viral Waves in 2020 and 2021 Among Canadian Adults. JAMA Network Open. 16 Feb 2022; 5(2):e2146798. doi:10.1001/jamanetworkopen.2021.46798.

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

In their CITF-funded research, Dr. Prabhat Jha and his team leading the Action to Beat Coronavirus (Ab-C) study estimated cumulative seroprevalence of SARS-CoV-2 during the first two viral waves. They found that among adults across Canada, seropositivity at a time when vaccines were not widely available rose from less than 2% after the first wave to up to 6.5% after the second. The study is now published in JAMA Network Open.

Key points:

  • Seroprevalence stood at 1.9% during the first viral wave and rose to about 5.4-6.5% during the second wave. The numbers were based on dried blood spot kits from almost 9,000 Canadians in May-September 2020 and nearly 7,000 Canadians in December 2020-March 2021.
  • The Atlantic provinces exhibited the lowest increase in seropositivity (from 1.3% to 2.8%).
  • Seroprevalence among self-described visible/ethnic minorities rose sharply from about 2% to over 7% from the first to the second wave.
  • Among individuals who were seropositive, 22% did not report having had any symptoms.
  • Infection-induced antibodies persisted for at least seven months.

Participants were recruited via the Angus Reid Forum, a nationwide panel of Canadian adults aged 18 and older. Following the online survey, participants who consented were mailed dried blood spot kits.

The authors suggest that although seroprevalence increased moderately among Canadians throughout the first two viral waves, it remained low at a time when vaccines were first deployed.