Less than 3% of Canadians were infected in the first year of the pandemic | Coronavirus

Statistics Canada sent kits to 48,000 Canadians to take blood samples and detect the presence of antibodies against COVID-19. About 12,000 of them agreed to prick their fingers to collect a blood sample, which was analyzed at the National Microbiology Laboratory in Winnipeg.

The proportion of people who develop antibodies is called the seroprevalence of antibodies against SARS-CoV-2. It is possible to determine whether the antibodies have developed as a result of an infection or a vaccine.

In addition to the 2.6% of infected Canadians, 1% developed antibodies as a result of a vaccine. Thus, 3.6% of Canadians had developed antibodies by early 2021, says Statistics Canada.

It should be noted that the blood samples were collected between November 2020 and April 2021, but that the majority of the data were collected in January and February 2021. The vaccination campaign was only just beginning and Canada experienced a significant wave of infections. in April and May. Thus, the seroprevalence rate to date is higher, says Statistics Canada.

Statistics Canada indicates that one in three Canadians who have developed antibodies against SARS-CoV-2 following an infection had never been tested before. So the majority of these people probably did not know they had had COVID-19.

In fact, 76.6% of people who had antibodies caused by an infection say they never had any symptoms. According to Statistics Canada, this data confirms that asymptomatic spread has contributed to infection rates.

The seroprevalence rate following infection is highest in Alberta (4%) and Quebec (3.2%). In British Columbia, less than 2% of people have been infected, according to Statistics Canada estimates. In the Atlantic provinces, the rate of seroprevalence of antibodies following an infection is very low (0.5%), a sign of the severe public health measures put in place to curb the pandemic.

In the Atlantic and Territories regions, approximately one in five residents would have developed antibodies following vaccination.

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The seroprevalence of antibodies following a previous infection is similar in males and females.

However, the number of women who developed antibodies due to vaccination (1.5%) is almost four times higher than for men (0.4%). Statistics Canada recalls that at the start of the vaccination campaign, women – many of whom work in the health sector – were much more likely than men to have been vaccinated, which could explain this difference.

Younger people also have a higher rate of seroprevalence of antibodies following a previous infection than older people. The rate is 3.3% among those aged 1 to 19, compared to 1.4% among those aged 60 and over. These figures do not include people living in retirement homes or long-term care facilities.

In young people, almost all of the antibodies have arisen as a result of infection with COVID-19. Remember that this age group is not yet eligible for vaccination.

Among Canadian adults aged 20 and over who have developed antibodies, about one in three adults developed them following a vaccination.

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It is also estimated that the proportion of Canadians belonging to a visible minority (4.3%) who have developed antibodies after infection is almost double that of Canadians who do not belong to a visible minority (2.1%). In addition, the percentage of visible minorities who developed antibodies following vaccination is half that of non-visible minority groups.

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Two studies that show a low seroprevalence rate

Public health measures have helped reduce the number of infected Canadians, says Dr. Jha.

Photo: The Canadian Press / PATRICK DOYLE

The prevalence rate calculated by Statistics Canada is a little lower than that of the current Ab-C study by Dr. Prabhat Jha, in collaboration with the Angus Reid Forum.

Dr. Jha and his team asked nearly 10,000 Canadians to provide a blood sample – much like Statistics Canada did. The epidemiologist explains that the two studies were done over a different period of time, so the rates may vary. They nevertheless arrived at several similar findings.

We had no idea at the start of the pandemic whether 25% or 15% of Canadians had been infected, says Dr Jha, who is director of Centre for Global Health Research, at St. Michael’s Hospital, and Professor of Epidemiology at the From the Lana School of Public Health, University of Toronto.

To ensure better representation of Canadian demographics, Dr. Jha’s team made sure to select participants from every federal riding across the country.

Sylvie Lemieux is one of the participants in this survey.

I thought to myself that it would be interesting to know if I had had COVID-19 without having any symptoms and I thought to myself that it would have value for research, she said, adding that the process was straightforward. The Quebecer sent two samples and on two occasions her test indicated that he was unlikely that she was infected. I telecommute and was so careful I don’t know how I would have caught it!

During the first sampling – which corresponds to spring, summer and fall 2020 – Dr. Jha determined that 2% of Canadians had been infected with COVID-19.

We were a little surprised by this low rate of seroprevalence, but it agrees with the fact that we were in confinement.

A quote from:Prabhat Jha, Epidemiologist, University of Toronto

In their second sampling – in January and February 2021 – this figure rose to around 5%.

Only the Atlantic provinces recorded a lower prevalence in the second wave, at 2-3%. Dr Jha explains this difference by the fact that travel to these provinces was very limited, which slowed down the spread of the virus.

Like the Statistics Canada survey, the figures from this study also show that tens of thousands of Canadians were infected – especially young adults – without knowing it. The number of asymptomatic people is quite high, says Dr Jha, adding that these people unknowingly contributed to the transmission of the virus.

As of September 1, Dr. Jha estimated that one million Canadians had already been infected. At that time, the official toll showed around 130,000 infections confirmed by screening. As of February 2021, Dr. Jha estimated that more than 1.5 million Canadians had been infected, while the official toll was less than 900,000 confirmed infections.

Our data suggests that confirmed cases are about half of the reality. It might sound like a lot, but it’s really not as much as other countries.

A quote from:Prabhat Jha, Epidemiologist, University of Toronto

Prevalence rates range from 1% in Iceland, 6% in the UK, and 10% in the US (New window) and even up to 15% in France (New window) .

Dr Jha believes Canada has been successful in doing more screening tests to confirm infections, which may explain why the total number of cases is closer to the estimated prevalence than elsewhere in the world.

Some reports, such as that of Héma-Québec, which estimate that 10% of Quebecers were infected between the start of the pandemic and the month of March 2021, may not be as precise, indicates Dr. Jha. These samples come from people who have donated blood, and these people do not necessarily represent the entire population.

Low prevalence, good news?

Dr. Prabhat Jha analyzed samples from thousands of Canadians to study the seroprevalence of COVID-19 in the country.

Photo : Unity Health Toronto

Dr Jha says the low prevalence of COVID-19 in Canada demonstrates that the country has managed to minimize the number of cases thanks to strict public health measures.

The bad news is that with so few Canadians infected and still susceptible to it, the only way out of the pandemic is with mass vaccination, says Dr. Jha.

Another good news: of people who showed antibodies after infection, 60-95% still had them seven months later. This suggests that the viral infection that causes COVID-19 leads to a long-lasting immune response, says Dr Jha.

This week, Dr. Jha’s team will send new tests to participants as part of the third phase of the study. Will we see rates go up to 10%? More? It’s to do, he said.

The results of these new blood tests will not only monitor the antibodies, but also see the long-term effectiveness of the vaccines.

Dr Jha believes that the blood samples received will also be used in the months and years to come to better understand SARS-CoV-2 and its long-term effects.

There is still a lot we don’t know about the disease and why some people are asymptomatic.

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