Preprints with The Lancet is part of SSRN´s First Look, a place where journals identify content of interest prior to publication. Authors have opted in at submission to The Lancet family of journals to post their preprints on Preprints with The Lancet. The usual SSRN checks and a Lancet-specific check for appropriateness and transparency have been applied. Preprints available here are not Lancet publications or necessarily under review with a Lancet journal. These preprints are early stage research papers that have not been peer-reviewed. The findings should not be used for clinical or public health decision making and should not be presented to a lay audience without highlighting that they are preliminary and have not been peer-reviewed. For more information on this collaboration, see the comments published in The Lancet about the trial period, and our decision to make this a permanent offering, or visit The Lancet´s FAQ page, and for any feedback please contact firstname.lastname@example.org.
SARS-CoV-2 Seroprevalence During the First and Second Pandemic Waves in Canada
Background: The prevalence of infection in Canada’s COVID-19 viral waves, the predictors of infection, and the durability of antibody responses to infection remain undocumented.
Methods: We organized serial online surveys of a representative group of Canadian adults about their COVID experience in the first (n=19 994; April-July 2020) and second viral wave (n=14 621; October 2020-March 2021). We paired these with IgG analysis of SARS-CoV-2 seroprevalence in self-collected dried blood spots after the first (n=8967) and second (n=7102) waves.
Findings: Canada’s cumulative seroprevalence of SARS-CoV-2 among unvaccinated adults rose from ~2% after the first wave to 7% after the second. The seropositivity pattern was heterogeneous demographically and geographically during the first wave, but more homogeneous by the second (except in the four Atlantic Provinces, cumulative seroprevalence ~3%). Seroprevalence among visible minorities rose sharply from about 2% to >8% from the first to second wave. About a quarter of those reporting COVID symptoms during the second wave were seropositive, and in both waves the odds ratio (OR) of seropositivity for COVID symptoms exceeded six. About one-fifth of seropositives reported no symptoms. Of 134 seropositive adults in the first wave who were retested after the second, 83% (111) remained seropositive at least seven months later. Current smokers and people with a history of diabetes had lower ORs of infection. We calculated the absolute numbers of seropositive adults nationwide, which nearly quadrupled from 0.57 million to 1.90 million, with the largest increases among older adults. Infection fatality rates fell from 3.7 to 2.6/1000 infections, most notably at older ages.
Interpretation: Canada’s COVID pandemic grew substantially between the first and second viral waves. Home-based DBS collection offers a practicable way to document evolving demographic and geographic patterns and to assess the levels and durability of population immunity, including from SARS-CoV-2 vaccination.
Funding: Pfizer Global Medical, Unity Health Foundation, and the Canadian COVID-19 Immunity Task Force.
Declaration of Interest: None to declare.
Ethical Approval: The Ab-C study was approved by the Unity Health Toronto Ethics Review Board.
Tang, Xuyang and Sharma, Abha and Pasic, Maria and Brown, Patrick and Colwill, Karen and Colwill, Karen and Gelband, Hellen and Birnboim, Chaim and Nagelkerke, Nico and Bogoch, Isaac and Bansal, Aiyush and Newcombe, Leslie and Slater, Justin and Rodriguez, Peter and Huang, Guowen and Fu, Sze Hang and Meh, Catherine and Wu, Chee Nee and Kaul, Rupert and Langlois, Marc-André and Morawski, Ed and Hollander, Andy and Eliopoulos, Demetre and Aloi, Benjamin and Tam, Teresa and Abe, Kento and Rathod, Bhavisha and Fazel-Zarandi, Mahya and Wang, Jenny and Wang, Jenny and Iskilova, Mariam and Pasculescu, Adrian and Pasculescu, Adrian and Caldwell, Lauren and Caldwell, Lauren and Barrios-Rodiles, Miriam and Mohammed-Ali, Zahraa and Vas, Nandita and Santhanam, Divya Raman and Cho, Eo Rin and Qu, Kathleen and Jha, Vedika and Suraweera, Wilson and Malhotra, Varsha and Mastali, Kathy and Wen, Richard and Sinha, Samir and Reid, Angus and Gingras, Anne-Claude and Chakraborty, Pranesh and Slutsky, Arthur S. and Jha, Prabhat, SARS-CoV-2 Seroprevalence During the First and Second Pandemic Waves in Canada. Available at SSRN: https://ssrn.com/abstract=3903944 or http://dx.doi.org/10.2139/ssrn.3903944