Surveilling prospective population cohorts for COVID 19: Prevalence and outcomes in Canada

Multiple people shot from above forming the shape of a virus

In Canada, as of December 11th, 2022, provincial testing data has confirmed 4.38 million cases of COVID-19 infection and 48,494 deaths, although it's estimated that approximately 50% of the population has now been infected.

Our understanding of who is most vulnerable to severe COVID-19 disease has evolved, but data suggests that increasing age and obesity are the strongest risk factors, and that even moderately excess weight may increase the risk of severe disease. Those with serious underlying health conditions, including hypertension, cardiovascular disease, type 2 diabetes, cancer, and chronic obstructive pulmonary disease are also at increased risk.

Victoria Kirsh, Assistant Professor in the Dalla Lana School of Public Health at the University of Toronto, is leading a study leveraging major prior investments into Canadian health platforms, to enable the real-time assessment of population susceptibility and prevalence, and risk factors associated with severity of COVID-19 infection.

“The relative importance of different underlying health conditions remains unclear from the research to date, some of which is hampered by inadequate adjustment for important confounding factors and under-reporting of pre-existing conditions,” says Professor Kirsh. “Data on lifestyle risk factors are scarce. Also, Canada's third coronavirus wave affected young people more severely than before and infections are escalating, driven by variants; it is unclear if the risk factors for severe infection during the first and second waves of the pandemic differ from those in the third and fourth.”

The project will use data collected through the Canadian Partnership for Tomorrow’s Health (CanPath) collection of cohort studies, including the Ontario Health Study, BC Generations Project and Alberta’s Tomorrow Project. In 2020 the CanPath cohorts administered a harmonized and comprehensive COVID-19 questionnaire which collected information about a variety of factors including demographics, COVID testing and symptoms, hospitalization, behaviours (e.g. travel, contact with a case, use of masks, etc.), existing health conditions and medications, and risk factors.

The questionnaire was administered only at one timepoint during the pandemic (in 2020) and not all participants completed it. Therefore, linkage with administrative health records is required to determine the full impact of COVID-19 incidence and prevalence in the cohort, and consequentially the effects on severe infection, hospitalization, etc. Population and clinical-level COVID-19 data across British Columbia, collected through the BC Generations Project baseline questionnaire and COVID-19 questionnaire, will be complemented by PopData’s linking of the cohort to seven administrative data sets from the BC Ministry of Health.

The study findings will be reported to the COVID-19 Immunity Task Force (CITF) and project stakeholders, including Health Canada, to make this data available to national and provincial health agencies.

This project utilized Health Data Research Network Canada’s Data Access Support Hub (DASH), designed to streamline and expedite pan-Canadian, multi-jurisdictional research, and received funding from CANPATH and the Canadian Institutes of Health Research (CIHR).