Concern about imbalances between the demand and the supply of vaccinations for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been raised, given worldwide demand, centralized manufacturing and limitations in the infrastructure for vaccine delivery and administration in Canada. The optimal strategy for vaccination allocation to maximize public health benefit in Canada is unclear. The first phase of Canada's vaccine rollout focused on those at the highest risk for being infected with or transmitting SARS-CoV-2, including long-term care residents and staff, older adults, adults in Indigenous communities and front-line health care workers. 1 However, debate continues about whether subsequent vaccinations (stages 2 and 3 in the National Advisory Committee on Immunization [NACI] schema) 2 should be prioritized solely on the basis of age (as age is the strongest risk factor for poor outcomes from coronavirus disease 2019 ), or whether a more complex rollout targeting those with other high-risk features (e.g., medical or exposure-related risk factors) may be preferable. 3 Vaccine prioritization questions are also related to the debate on whether to delay second doses so that as many people as possible receive at least 1 dose. 3,4 Substantial variability exists between the provinces and territories regarding current approaches to vaccination, with differing definitions of who qualifies as medically, geographically or occupationally "high risk." 5 To optimize vaccination strategies, we must first delineate what proportion of adults in Canada are at higher risk for severe outcomes if infected with SARS-CoV-2. A recent evaluation of data from the National Health and Nutrition Examination Survey (NHANES) reported that three-quarters of adults in the United States had 1 or more risk factors for severe COVID-19, as defined by the US Centers for Disease Control and Prevention (CDC). 6 We analyze the burden of risk factors in the Canadian population to complement analyses of provincial administrative data sets to better inform ongoing SARS-CoV-2 vaccination prioritization in Canada.
KEY POINTS• Debate continues about how best to prioritize vaccinations for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) once the most vulnerable older adults have been vaccinated.• Although age is the most important risk factor for severe (COVID-19), three-quarters of adults in Canada have at least 1 other risk factor for severe illness, and one-third have 2 or more risk factors, based on analysis of national survey data.
How common are risk factors for severe COVID-19 infection among communitydwelling adults in Canada?Although each Canadian province and territory can evaluate their administrative health data to identify the proportion of their population at risk for severe COVID-19, there are limitations to using such data to estimate disease frequencies, as they often underestimate the burden of chronic diseases that are predominantly managed in outpatient settings. 7,8 Moreover, some risk factors for severe COVID-...