Study suggests as few as 0.7% of adults have antibodies to SARS-CoV-2
Canadian Blood Services and Canada’s COVID-19 Immunity Task Force (CITF) are releasing final results of a collaborative nine-province SARS-CoV-2 seroprevalence study. This analysis, based on 37,373 blood samples from blood donor centres across Canada (except Quebec and the Territories), reveals that fewer than 1 per cent of Canadian blood donors tested positive for antibodies to the novel coronavirus. The blood samples were collected between May 9th and June 18th, 2020. The testing was funded by the Government of Canada via its COVID-19 Immunity Task Force.
Antibodies are a key indicator of past infection and can generally be detected within two weeks of the onset of infection. Thus, these results suggest that, by the end of May, as few as 0.7 per cent of healthy Canadians had been exposed to SARS-CoV-2, the virus causing COVID-19.
“We know that these results could underestimate true seroprevalence for two reasons,” states Professor Catherine Hankins, CITF Co-Chair. “First, antibody levels do decline rapidly and may have disappeared in some people by the time of testing. Second, blood donors in general are health-conscious and healthier than the general population,” she continues. “Nonetheless, these results once again tell us how few Canadians were infected by SARS-CoV-2 by the end of May. This shows that when all actors, especially individual citizens, follow good public health practices, the risk of infection diminishes considerably,” she adds.
That said, with the increasing number of COVID-19 cases now being seen in some parts of the country, these findings also point to the need for continued vigilance. “Global data suggest that population-wide infection rates estimated from SARS-CoV-2 antibodies are about 50% higher than those measured in blood donor samples. But even if we doubled or tripled the estimates from this study, there is little to no likelihood that levels of immunity in the population are high enough to slow down a second wave of COVID-19 infection,” says CITF Co-Chair Professor David Naylor. “As such, it’s critical to ramp-up testing and tracing capacity across the country to reduce risk in settings such as workplaces and schools, and to interrupt any chains of transmission quickly to prevent spread.”
“The results also have confirmed low seroprevalence in all provinces and cities across Canada,” points out Sheila O’Brien, Associate Director, Epidemiology & Surveillance at Canadian Blood Services. “Whereas Prince Edward Island and New Brunswick have the lowest seroprevalence at 0% and 0.26% respectively, Ontario showed the highest, with 0.96%.” (See table 1 below for provincial breakdown). Although not included in the Canadian Blood Services study, Quebec shows the highest seroprevalence in the country to date: Héma-Québec recently announced that their seroprevalence study revealed that 2.23% of Quebec blood donors were infected with the virus that causes COVID-19.
“When we take a look at selected cities across the country, Ottawa shows the highest percentage of people with SARS-CoV-2 antibodies with 1.29% seroprevalence, Toronto was found to have 1.07%, whereas Edmonton has the lowest percentage of positive tests at 0.38%,” says Professor Timothy Evans, CITF Executive Director. (See table 2 below for a breakdown of selected cities).
“Canadian Blood Services was uniquely positioned to help the CITF with Canada’s initial seroprevalence study, given our existing infrastructure, experience, and expertise, as well as that our donor base is reasonably representative of healthy Canadians between the ages of 17 and about 60,” says Dr. Graham Sher, Chief Executive Officer, Canadian Blood Services. “We are proud to contribute to Canada’s fight against COVID-19 in this way.” The CITF will be working with Canadian Blood Services and Héma-Québec to further validate these results by running blood donor samples on other antibody tests over the coming weeks.
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 THE COVID-19 IMMUNITY TASK FORCE
The Government of Canada launched the COVID-19 Immunity Task Force (CITF) in late April 2020 to track the spread of the virus in both the general population and priority populations in Canada. The Task Force also aims to shed light on immune responses to SARS-CoV-2 in a diversity of communities, age brackets, populations, and occupational groups across the nation. To generate this information, the Task Force is drawing on experts from universities and hospitals across Canada and working closely with provincial and territorial public health officials. For more information visit: www.covid19immunitytaskforce.ca
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