Study reveals children and youth had highest rates of SARS-CoV-2 infection in Canada before third waveVisible minorities twice as likely to have caught the virus

MONTREAL, July 07, 2021 (GLOBE NEWSWIRE) -- Canada’s most representative study to date investigating how many Canadians have antibodies to SARS-CoV-2, the virus causing COVID-19, reveals a mere 2.6% of Canadians tested between November 2020 and April 2021 had developed antibodies resulting from a past infection. Another 1% of Canadians had antibodies due to vaccination, reflecting the fact that vaccination was not widely available during the survey period. This brings the total percentage of Canadians with some form of immunity before the third wave to 3.6%. These data come from Statistics Canada’s Canadian COVID-19 Antibody and Health Survey (CCAHS), done in partnership with Canada’s COVID-19 Immunity Task Force (CITF), the Public Health Agency of Canada, and Health Canada.

“More than 10,000 Canadians, 1 year of age and older from across Canada participated in this study by sending a dried blood spot (DBS) sample and answering a questionnaire, making it highly representative of the people in this country,” explains Ron Gravel, Director at Statistics Canada and lead on the project. “The study includes data from all 10 provinces and three territories, people from both rural and urban areas, and Canadians with varied health status.”

“One of the most interesting findings is the fact that seniors – those not in long-term care – were not the ones to have had the most SARS-CoV-2 infections in Canada,” says Dr. Catherine Hankins, CITF Co-Chair. “Younger age groups – and especially children and adolescents - had higher rates of antibodies in their blood suggesting a past SARS-CoV-2 infection.”

“The overall seroprevalence of SARS-CoV-2 antibodies was 3.4% among children and youth 1 to 19 years of age between November and April 2021,” explains Mr. Gravel. “As vaccines had not yet been distributed to this age group at the time of the survey, nearly all of these children and youth had antibodies due to a previous infection. In comparison, 2.9% of Canadians 20 to 59 years of age, and 1.4% of Canadians 60 years of age and older, were found to have antibodies due to a past infection.” Estimates for the Canadian population 60 years of age and older do not include those living in an institutional setting, such as a retirement home or in a long-term care setting.

Overall antibody seroprevalence (the percentage of people with antibodies in their blood), including Canadians with both infection-acquired and vaccine-induced antibodies, was highest in adults 20 to 59 years of age (4.5%). Among those 60 years of age and older, overall antibody seroprevalence was 2.1%.

Visible minority Canadians more affected by the virus

Canadians belonging to visible minorities had a higher proportion of antibodies acquired through past infection (4.3%) compared to other Canadians (2.1%). This contributed to a higher overall SARS-CoV-2 antibody seroprevalence among visible minorities (4.8%) compared to other Canadians (3.3%).

“This study shows that Canadians belonging to visible minorities have had more SARS-CoV-2 infections,” explains Dr. Hankins. “Public health authorities, community groups, and employers must continue to focus efforts on ensuring they can receive two doses of vaccine.”

Many Canadians didn’t know they were previously infected

“About one in three (30.3%) Canadians who had antibodies due to a SARS-CoV-2 infection had never taken a PCR test - a nasal or throat swab test for an active infection,” reveals Mr. Gravel. Among those, 3 out of 4, (76.6%) indicated that it was because they never had symptoms.

“Asymptomatic infections are very real,” comments Dr. Hankins. “Many Canadians who tested positive for antibodies from a previous infection did not know they had COVID-19 and could very easily have spread it to others, although the numbers don’t tell us how much transmission there was. This reinforces that physical distancing measures and mask- wearing have been the best ways to control the virus, especially before the widespread distribution of vaccines.”

Antibody seroprevalence varied across the country

Before the third wave, the percentage of Canadians with antibodies (the seroprevalence) due to a previous infection was highest in Alberta (4.0%), followed by Quebec (3.2%), Saskatchewan (2.9%), Ontario (2.5%), Manitoba (2.4%) and British Columbia (1.6%). The Atlantic Provinces had only 0.5% seroprevalence due to past infection, while the number of residents in the Territories to have antibodies due to a past infection was too low to produce a reliable statistical estimate.

In addition to Canadians with antibodies due to a prior infection, about 33% of adults (more than 20 years of age) who tested positive for antibodies had antibodies from vaccination.

Antibody seroprevalence from both vaccination and past infection was highest in Alberta (5.6%), followed by Quebec (4.4%), Saskatchewan (4.1%), Ontario (3.3%), Manitoba (3.1%), British Columbia (2.4%) and finally the Atlantic provinces (1.3%).

Within the Territories and Atlantic region, most people with antibodies had acquired them through vaccination. Due to the early start of the vaccination campaign in the Territories, about 1 in 5 (21.1%) Territorial residents had SARS-CoV-2 antibodies due to vaccination.

“At no time has the role of better data been more important in driving better outcomes than during a pandemic,” said Anil Arora, Canada’s Chief Statistician, who leads Statistics Canada. “I wish to thank Canadians who voluntarily participated in this survey. They are playing an essential role in advancing the development of new diagnostic tools, treatments and clinical practices that could ultimately benefit all Canadians in the fight against COVID-19.”

Made-in-Canada testing technology

“Another really interesting aspect of this study is the use of dried blood spot (DBS) kits, also known as finger prick tests,” explains Dr. Hankins. “These test kits were sent to tens of thousands of Canadians in rural and urban parts of the country so they could give a blood sample from home by pricking their finger in a specific way. The CITF helped get this DBS method approved for use in Canada, which was important because Statistics Canada and other studies would not have been able to test Canadians in such a representative manner if they had had to draw blood the traditional way with a needle.”

The blood samples from the DBS kits were analyzed at the Gingras Toronto laboratory and the Langlois Ottawa laboratory using cutting-edge assays (tests) developed in Canada.

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The table “SARS-CoV-2 antibody seroprevalence in Canadians, by age group and sex” is now available. This table provides national – as well as regional or provincial – estimates of the prevalence of antibodies against SARS-CoV-2 among Canadians, by age group and sex.

Upcoming Townhall for more information

The CITF is hosting a townhall, in collaboration with Statistics Canada, open to all Canadians. Presenters from the CITF and Statistics Canada will provide more detailed data and will include an explanation of the CITF’s updated models regarding the progression of population immunity throughout the pandemic. “These data will further inform the CITF’s modelling efforts which will be updated for the townhall on July 15th,” says Dr. David Buckeridge, Scientific Lead, Data Management and Analysis for the CITF.

The event will take place on July 15, from noon to 1 p.m. EDT. The event is free and will be held via Zoom webinar. To register, send an email to media@covid19immunitytaskforce.ca.

About Statistics Canada

Statistics Canada produces statistics that help Canadians better understand their country—its population, resources, economy, society and culture. In addition to conducting a Census every five years, there are about 350 active surveys on virtually all aspects of Canadian life. Statistics Canada has accelerated data collection in response to the urgent need for information to help the country respond to, and recover from, the social and economic impacts of the COVID-19 pandemic in Canada.

Statistics Canada is highly committed to protecting the confidentiality of all information it collects and to ensuring that the information we deliver is timely, high quality and relevant to Canadians.

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 facilities 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 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: http://www.covid19immunitytaskforce.ca

Media contacts

COVID-19 Immunity Task Force/Vaccine Surveillance Reference Group
media@covid19immunitytaskforce.ca
Rebecca Burns
Cell: +1.438.871.8763
Caroline Phaneuf
Cell: +1.514.444.4532

Statistics Canada - Media Relations
Phone: +1.613.951.4636
Email: statcan.mediahotline-ligneinfomedias.statcan@canada.ca

Table 1                  
National SARS-CoV-2 Antibody Seroprevalence Estimates, by antibody seroprevalence type and sex      
                   
Sex Overall Antibody seroprevalence percentage Low 95% Confidence Interval High 95% Confidence Interval Antibody seroprevalence due to infection percentage Low 95% Confidence Interval High 95% Confidence Interval Antibody seroprevalence due to vaccination percentage Low 95% Confidence Interval High 95% Confidence Interval
Both Sexes 3.6 2.6 4.2 2.6 1.6 3.2 1.0 0 1.3
Males 3.3 2.2 4.1 2.8 1.8 3.6 0.4 0 0.6
Females 3.9 2.8 4.7 2.4 1.3 3.0 1.5 0.5 2.0
Table 2                
National SARS-CoV-2 Antibody Seroprevalence Estimates, by antibody seroprevalence type and age group  
                 
Age Group Overall
Antibody seroprevalence percentage
Low 95% Confidence Interval High 95% Confidence Interval Antibody seroprevalence due to infection percentage Low 95% Confidence Interval High 95% Confidence Interval Antibody seroprevalence due to vaccination percentage Low 95% Confidence Interval High 95% Confidence Interval
All age groups 3.6 2.6 4.2 2.6 1.6 3.2 1.0 0 1.3
1 to 19 years 3.4 2.2 4.6 3.3 2.1 4.5 X X X
20 to 59 years 4.5 3.3 5.5 2.9 1.8 3.7 1.6 0.6 2.0
60 years or older 2.1 1.0 2.7 1.4 0.4 1.9 0.7 0 1.2

X Data suppressed to meet the confidentiality requirement of The Statistics Act.

Table 3                  
Provincial or Regional SARS-CoV-2 Antibody Seroprevalence Estimates, by antibody seroprevalence type
                   
Province or Region Overall Antibody seroprevalence percentage Low 95% Confidence Interval High 95% Confidence Interval Antibody seroprevalence due to infection percentage Low 95% Confidence Interval High 95% Confidence Interval Antibody seroprevalence due to vaccination percentage Low 95% Confidence Interval High 95% Confidence Interval
Canada 3.6 2.6 4.2 2.6 1.6 3.2 1.0 0 1.3
Atlantic Region 1.3 0.3 1.8 0.5 0 0.7 0.9 0 1.3
Quebec 4.4 3.2 5.4 3.2 2.1 4.1 1.2 0.2 1.7
Ontario 3.3 1.6 5.5 2.5 1.1 4.4 0.8 0 1.9
Manitoba 3.1 1.8 4.5 2.4 1.2 3.6 0.7 0 1.5
Saskatchewan 4.1 2.6 5.7 2.9 1.6 4.3 1.2 0.1 2.2
Alberta 5.6 4.0 7.4 4.0 2.6 5.7 1.6 0.3 3.4
British Columbia 2.4 1.1 3.9 1.6 0.5 2.9 0.8 0 1.7
Territories Region 21.1 17.6 25.0 0 0 0.8 21.1 17.6 25.0

Note: Some seroprevalence estimates may not add correctly due to rounding.

Table 4                  
National SARS-CoV-2 antibody seroprevalence estimates, by antibody seroprevalence type and visible minority status    
                   
Visible Minority Status Antibody seroprevalence overall percentage Low 95% Confidence Interval High 95% Confidence Interval Antibody seroprevalence due to infection percentage Low 95% Confidence Interval High 95% Confidence Interval Antibody seroprevalence due to vaccination percentage Low 95% Confidence Interval High 95% Confidence Interval
Visible Minority 4.8 3.1 6.8 4.3 2.6 6.3 0.5 0 1.2
Not a Visible Minority 3.3 2.3 3.9 2.1 1.1 2.6 1.2 0.2 1.5


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