MONTREAL, July 6, 2022 – An analysis of data from 21 studies, funded by the Government of Canada through its COVID-19 Immunity Task Force (CITF) and that relied on blood testing, provides a clearer picture of the massive scale of the Omicron wave in Canada. Before the arrival of the Omicron variant, approximately 7% of Canadians had infection-acquired antibodies to SARS-CoV-2, the virus that causes COVID-19. Between December 2021 and May 2022, the proportion rose by 45% of Canadians having antibodies to SARS-CoV-2 infection (see Figure 1 below). A fuller account of the analysis can be found online here.
“Omicron has been a tsunami,” states CITF Executive Director Dr. Tim Evans. “Across the country, our analysis of the data suggests that 17 million Canadians had an Omicron infection in the period December to May, for an average of more than 100,000 infections per day. New sublineages in the Omicron line have been continuing to spread since then, and the percentage of Canadians who have had a SARS-CoV-2 infection is now likely well above 50%.”
All provinces affected
The number of people with signs of a previous infection in their blood (infection-acquired seroprevalence) has increased steeply during the Omicron wave in every province (Figure 2). By the end of May, the proportion of people with evidence of previous infection was 50-60% in the Western and Central provinces. Although Atlantic Canada retained the lowest seropositivity due to infection, it had the largest relative increase in seroprevalence and reached over 35%.
Omicron affected all ages — but the younger and less vaccinated populations most!
Analysis of blood donations made to Canadian Blood Services (which provides the CITF an update every two weeks) showed that the highest levels of seropositivity due to infection were in young adults, with about 65% having antibodies by the last week of May. Rates of seropositivity due to infection decreased with increasing age: 25-39 (57%), 40-59 (51%), and 60+ (31%) (Figure 3).
“Through sheer numbers of infections, the Omicron variant exacted a substantial toll in services and lives disrupted, as well as hospitalizations and deaths. It clearly did not spare healthy young Canadians” says CITF Co-Chair Dr. Catherine Hankins. “As well, we’re still learning about who gets a post COVID-19 condition or long COVID, why, and the repercussions. This summer may be free of public health restrictions, but Omicron is still spreading so masking and distancing are smart in risky settings. To minimize further disruptions to our lives, Canada has to track the situation closely as it evolves. We all need to respond in a timely way as this virus does not have a seasonal pattern, like the other respiratory viruses we expect when everyone heads back to work or school in the autumn.”
“Millions of Canadians now have hybrid immunity from a combination of COVID-19 vaccines and an infection. Unfortunately, emerging evidence suggests that most of these individuals remain at risk of re-infection with viruses in the Omicron lineage,” explains CITF Co-Chair Dr. David Naylor. He adds “Newer vaccines may improve coverage against infection. However, we still have millions of adults who haven’t had a third shot and should get one to consolidate their protection against serious disease. More generally, all Canadians should stay alert for the latest public health guidance on COVID-19 vaccines and make sure their coverage is up to date for the fall season.”
About the COVID-19 Immunity Task Force
The Government of Canada established the COVID-19 Immunity Task Force (CITF) in late April 2020 to catalyze, support, and harmonize research on SARS-CoV-2 immunity for federal, provincial, and territorial decision-makers in their efforts to protect Canadians and minimize the impact of the COVID-19. The Task Force and its Secretariat work closely with a range of partners, including governments, public health agencies, institutions, health organizations, research teams, and other task forces, engaging communities and stakeholders. To date, the CITF has supported over 100 studies across Canada that are generating insights on the levels, trends, nature, and duration of immunity arising from SARS-CoV-2 infection and COVID-19 vaccination. The CITF is overseen by an Executive Committee of volunteers that includes leading scientists and policymakers from across Canada.
Figure 1. Anti-nucleocapsid seroprevalence (infection-acquired seropositivity) for all Canadian provinces for all age groups, combined
Figure 2. Anti-nucleocapsid seroprevalence (infection-acquired seropositivity) estimates by province
Figure 3. Anti-nucleocapsid seroprevalence (infection-acquired seropositivity) estimates by median age
The views expressed herein do not necessarily represent the views of the Public Health Agency of Canada.