Results from the latest Canadian Blood Services and Héma-Québec studies, which together cover all 10 provinces, confirm that from coast-to-coast, Canada’s overall levels of seroprevalence due to SARS-CoV-2 infection remained very low earlier this year, as the roll-out of vaccines started ramping up. The Canadian Blood Donor Services study is supported by the Government of Canada, through its COVID-19 Immunity Task Force (CITF), whereas the Héma-Québec study is supported by Quebec’s public health institute, Institut national de santé publique du Québec (INSPQ). All organizations have been working collaboratively to provide Canadians and policymakers with a comprehensive assessment of infection and immunity in Canada and to prepare the groundwork to track how long immunity through vaccination lasts.
Overall Canadian Seroprevalence and Regional Differences
Canadian Blood Services data, based on blood donors, show that the seroprevalence due to infection (the number of people who had antibodies to SARS-CoV-2 due to a past infection) in Canadian provinces excluding Quebec was 2.2% in January. In contrast, in Québec, between January and March 2021, Héma-Québec data indicate that seroprevalence from infections was 10.5%. In this province, the roll out of vaccination resulted in an increase of this number of up to 14.7% of the population with some immunity.
“The low rates of seroprevalence across all 10 provinces show Canadians have been doing a great job following public health guidelines,” says CITF Executive Director Dr. Tim Evans. “But they also confirm that without high vaccine uptake, we are far from ending this pandemic.”
“The evolution of the pandemic has differed across the country,” adds Dr. David Buckeridge, Scientific Lead, Data Management and Analysis for the CITF. “That is clear from our statistical model that combines the results from Héma-Québec and Canadian Blood Services with other epidemiological indicators. However, the bottom line is that the level of immunity from infection remains low in Canada.”
“The Atlantic provinces have been doing a tremendous job at protecting people from SARS-CoV-2,” says Dr. Sheila O’Brien, Associate Director of Epidemiology and Surveillance at Canadian Blood Services and the study’s primary investigator. “By January 2021, nearly a year into the pandemic, of those who donated blood, the data still shows an exceptionally low percentage of people with antibodies resulting from SARS-CoV-2 infection: 0% in Prince Edward Island and Newfoundland, 0.18% in New Brunswick, and 0.39% in Nova Scotia.”
The Prairie provinces, in contrast, had the highest seroprevalence with Manitoba at 5.4%, Alberta at 4.0%, and Saskatchewan at 3.5% in January 2021. “If we had looked at the percentage of Quebecers who had antibodies due to infection in January, our numbers might have been similar to the Prairie provinces data from Canadian Blood Services,” says Dr. Marc Germain, Vice-President of Medical Affairs and Innovation at Héma-Québec and the study’s lead researcher.
In Ontario, 1.9% of blood donors had antibodies to SARS-CoV-2 due to a previous infection, and in British Columbia the percentage was 1.6%.
Reports Highlight At-Risk Communities
“These reports also draw attention to the increased risk of infection among racialized communities, those living in poorer neighbourhoods, and young Canadians, aged 17-24, making them high priorities for vaccination and efforts to prevent the spread of infection,” says Dr. Evans.
Increasing racial inequality in infection and vaccination
Data from both Canadian Blood Services and Héma-Québec show the pandemic is affecting racialized Canadians twice as much as self-declared Caucasian Canadians.
“Consistently, from the beginning of the pandemic, seroprevalence rates were higher among racialized populations compared to donors who self-identified as Caucasian. By January 2021, the seroprevalence was about double in racialized donors,” comments Dr. O’Brien.
A similar trend was observed in Quebec although further studies would be needed to get a better understanding of the situation. “Non-vaccinated blood donors self-identifying as non-Caucasian had seroprevalence rates of 19.3%, whereas only 9.5% of non-vaccinated Caucasian blood donors had antibodies to SARS-CoV-2,” states Dr. Germain. “That means twice as many non-Caucasian blood donors had antibodies because of infection compared to Caucasians.”
Increasing risk of infection in poorer neighbourhoods
In wave 1, seroprevalence was similar in neighbourhoods of all socioeconomic indexes. However, donors living in the most materially deprived neighbourhoods (based on postal codes) saw seroprevalence grow much more rapidly over time. In January 2021, seroprevalence among donors living in the most affluent neighbourhoods was 1.2%, while for those living in the most materially deprived areas was 4.0%.
In Quebec, a similar trend, although not as evident, was also observed. Whereas 15.0% of blood donors from the most affluent neighbourhoods had antibodies due to either an infection or vaccination, 17.3% of donors from the poorest neighbourhoods had antibodies.
Increased risk in the 17-24 age group
“Canadian Blood Services found infection rates among donors aged 17-24 years-old increased significantly from 0.8% during wave 1 to 3.0% in November 2020 and to 3.5% in January 2021,” says Dr. O’Brien.
“In Quebec, the 18-24 age group had the highest seroprevalence by far with 19% of blood donors in this age group having antibodies due to infection or vaccination,” says Dr. Germain. “That compares to a seroprevalence of 9.8% for the 60-69 age group.”
“The disproportionate number of infections in young people is likely a product of both their front-line work environments and more at-risk behaviours,” says Dr. Evans. “But this also reflects effective public health efforts to protect seniors in the second wave. The immediate priority is to encourage this younger age group to get vaccinated now that they are eligible in most provinces.”
Serosurveys will help to determine how long immunity lasts
These serosurveys are confirming previous research that vaccines are working and producing antibodies in people. “We’re seeing the number of antibodies rising in people just days after being vaccinated,” says Dr. Germain. Interestingly, both Canadian Blood Services and Héma-Québec found that about 95% of donors who had been vaccinated at least two weeks before donating blood had vaccine-induced antibodies.
“What we do not yet know is how long immunity from infection or from vaccines lasts,” says Dr. Evans. “Continuing these serosurveys of blood donors will signal when people in different age groups start to show less immunity, which may help to inform the best timing of the possible need for a booster vaccination.”
In effect, Héma-Québec’s data shows antibodies are waning. “Of the 109 people who tested positive for antibodies in wave 1, 32 of them no longer tested positive for antibodies 7-10 months later,” says Dr. Germain. “That’s a seroreversion rate of 29%. If we look at people who had more severe cases of COVID-19 and therefore likely had more antibodies at the time of infection, 14% lost their antibodies within a year. This shows that antibodies from infection do not necessarily remain in people’s blood forever and suggests boosters might be needed.”
Blood donors as a measure of overall seroprevalence
“These studies can play a pivotal role in helping public health authorities assess policies,” says Dr. Evans. “They allow us to see the real picture of the epidemic on a continuous basis. They are also useful in that they point to policy blind spots such as faster growth in infection in racialized communities.”
“Our serosurveys offer important insight into the effects of the pandemic in Canada,” says Dr. Graham Sher, CEO of Canadian Blood Services. “It is important to acknowledge that serosurveys based on blood donors do have limitations. Blood donors self-select to be blood donors and donation selection criteria ensure blood donors are healthy, so caution should be exercised in extrapolating findings to all adult Canadians.” Other factors include that in some areas, access to a donation clinic or time to donate blood may be limited. There are also fewer young or elderly blood donors compared to the general population.
“That said, since extra blood samples are systematically collected from each donation, as blood collection activities are held in most regions and as we have the laboratories to carry out tests, we are uniquely positioned to help inform public health authorities as they plan the next steps and phases of the pandemic,” says Nathalie Fagnan, President and Chief Executive Officer of Héma-Québec.
“Indeed, when we use statistical modelling to triangulate across available data, the estimates of seroprevalence from blood donors are consistent with other epidemiological indicators such as deaths,” adds Dr. David Buckeridge. “The blood bank estimates are extremely valuable for monitoring the overall seroprevalence in Canada.”
About the Partnership
When the Government of Canada established the CITF in late April 2020, Canadian Blood Services and Héma-Québec reached out to offer their assistance. Canadian Blood Services and Héma-Québec routinely test blood donations and both organizations also regularly contribute to ethics-approved research studies like this one.
While the donation selection criteria ensure blood donors are healthy, caution should be exercised in extrapolating findings to all healthy adult Canadians because blood donors self-select to be blood donors, in some areas access to a donation clinic may be limited, and there are fewer elderly donors who donate blood compared to the general population.
About Canadian Blood Services
Canadian Blood Services is a not-for-profit charitable organization. Regulated by Health Canada as a biologics manufacturer and primarily funded by the provincial and territorial ministries of health, Canadian Blood Services operates with a national scope, infrastructure and governance that make it unique within Canadian healthcare. In the domain of blood, plasma, and stem cells, Canadian Blood Services provides services for patients on behalf of all provincial and territorial governments, except Quebec. The national transplant registry for interprovincial organ sharing and related programs reaches into all provinces and territories, as a biological lifeline for Canadians. For more information visit: blood.ca
Héma-Québec acts as a supplier of human tissues intended for transplants (including cutaneous tissues, heart valves, and musculoskeletal tissues, such as tendons and bones), and makes them available to Québec hospitals. Héma-Québec retrieves and prepares eye tissues for use in cornea transplants.
Héma-Québec’s mission is to efficiently meet the needs of the Québec population for quality blood and other biological products of human origin. Héma-Québec encompasses 1,500 employees and nearly 255,000 blood, stem cell, mother’s milk and human tissue donors, in addition to thousands of blood drive volunteers. Each year, Héma-Québec delivers some 820,000 human biological products to Québec hospitals to meet the needs of patients. For more information visit: hema-quebec.qc.ca
About the COVID-19 Immunity Task Force
The Government of Canada established the COVID-19 Immunity Task Force in late April 2020. The Task Force is overseen by a Leadership Group of volunteers that includes leading Canadian scientists and experts from universities and healthcare homes across Canada who are focused on understanding the nature of immunity arising from the novel coronavirus that causes COVID-19. To that end, the CITF is supporting numerous studies to determine the extent of SARS-CoV-2 infection in Canada (in the general population as well as in specific communities and priority populations), understand the nature of immunity following infection, develop improved antibody testing methods, and help monitor the effectiveness and safety of vaccines as they are rolled out across Canada. The Task Force and its Secretariat accordingly work closely with a range of partners, including governments, public health agencies, institutions, health organizations, research teams, other task forces, and engages communities and stakeholders. Most recently, the Task Force has been asked to support vaccine surveillance, effectiveness and safety as part of its overall objective to generate data and ideas that inform interventions aimed at slowing—and ultimately stopping—the spread of SARS-CoV-2 in Canada. For more information visit: www.covid19immunitytaskforce.ca