In this study partially funded by the CITF and published in Microbiology Spectrum, researchers from Alberta Precision Laboratories collected blood samples from June 2020 to January 2021 to determine the prevalence of SARS-CoV-2 antibodies in Alberta, by assessing a total of 93,993 individual patient samples. While the prevalence of antibodies in June 2020 was very low (0.92%), prevalence increased to 4.63% in January 2021. As many as 53.7% of individuals who had positive antibodies did not know that they had previously been infected.

Researchers from Alberta Precision Laboratories carried out monthly SARS-CoV-2 antibody testing during five-day periods from June 2020 to January 2021. Information on sociodemographic factors, as well as previous COVID-19 diagnosis were also collected. Over the course of the study, 93,993 individual patient samples were tested.

Alberta’s first COVID-19 wave peaked on April 24, 2020, with antibody tests in June indicating that only 0.92% of samples were positive. However, antibody positivity increased to 2.47% in December 2020, followed by 4.63% in January (adjusted by age and sex). Overall, 1245 tests were positive for SARS-CoV-2 antibodies during the testing period, representing a prevalence of 1.75% (adjusted for age and sex).

Key findings

  • Researchers observed a higher rate in antibody positivity among those in the 0- to 9- year age group (2.71%), followed by those in the 20- to 29-year age group (1.58%), when compared to those in the 70- to 79-year age group (0.79%).
  • The factors associated with antibody positivity included: lower household income, large household size, education levels of secondary school or lower, and being a racialized Canadian.
  • 7% of individuals with antibodies did not have a previous COVID-19 diagnosis, indicating the potentially high level of undetected cases.

The paper provides context on where infections were occurring, and which populations were disproportionately affected. These findings can continue to help guide public health decisions aimed at mitigating SARS-CoV-2 transmission.

 

Charlton CL, Nguyen LT, Bailey A, Fenton J, Plitt SS, Marohn C, Lau C, Hinshaw D, Lutsiak C, Simmonds K, Kanji JN, Zelyas N, Lee N, Mengel M, Tipples G. Pre-Vaccine Positivity of SARS-CoV-2 Antibodies in Alberta, Canada during the First Two Waves of the COVID-19 Pandemic. Microbiol Spectr. 2021 Sep 3;9(1):e0029121. doi: 10.1128/Spectrum.00291-21.