TORONTO — The number of Canadian adults infected with COVID-19 has tripled during the fifth wave of the pandemic compared to the total number of adults infected in the previous four waves, according to a new study led by Toronto researchers.
More than 5,000 Canadian adults — members of the Angus Reid Forum, a public exploratory group — participated in the Phase 4 Action to Beat Coronavirus (Ab-C) study. The study results were published as a letter to the editor in the New England Journal of Medicine Wednesday.
The adult participants performed the dried blood spot test themselves between January 15 and March 15, 2022 and sent blood samples to the researchers for analysis. The research team then tested the samples for antibodies related to COVID-19.
From these findings, the researchers found that nearly 30 percent of Canadian adults were infected during the first wave of omicron infection compared to about 10 percent of those infected in the previous four waves.
Of that fifth wave of infections, the study notes, 1 million were among the country’s 2.3 million unvaccinated adults — representing 40 percent of all unvaccinated adults.
Patrick Brown, lead author of the Ab-C study and a biostatistician at the Center for Global Health Research at St. Michael’s Hospital, said the study aims to portray a “full and representative picture” of COVID-19 in the country in the absence of large-scale PCR testing and tracking of COVID data. -19.
“This is very important for us to be able to understand COVID in the population,” he said in a phone interview on Wednesday.
“The testing data is incomplete and we have essentially stopped PCR testing for the most part in Canada, or in Ontario, at least, so having a representative sample of people receiving these test kits is very important to know how much COVID there was and how much immunity we have.” among the population.”
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The study also found that antibody levels were significantly lower among adults with just two doses of the COVID-19 vaccine compared to those who had three doses, meaning those who took three doses had stronger immunity to the virus.
Among the unvaccinated population, Brown noted, including those who had contracted COVID-19, their antibody levels were “completely” lower than in people who had taken three doses of the vaccine.
“(In) Canada, we’ve had a little less COVID-19 than some other countries, especially the United States. We have less natural protection and we’re really dependent on vaccines in Canada to build immunity in our population,” he said.
“Certainly three doses plus infection was the ultimate protection, but three doses of the vaccine definitely gave a very good amount of protection – a huge improvement over just two doses.”
The Ab-C study is a collaboration between Unity Health Toronto, the University of Toronto’s Dalla Lana School of Public Health, the Angus Reid Institute and the Lunenfeld-Tanenbaum Research Institute at Sinai Health. It was funded by the federal government through the COVID-19 Immunity Task Force.
The team of researchers has been tracking the pandemic in Canada with periodic live-trial surveys and blood sample collection since May 2020.
Brown said the next phase of the study is already underway. The team began scanning nearly 1,300 Canadian adults who did not have a primary Omicron variant known as BA.1 to determine if they had an Omicron variant called BA.2 from March to June 2022.
“We are preparing the test groups now to send our team of people we have been back to a few times, and this will be the fifth round of tests we are sending them to better understand the second wave of Omicron,” he said.
“We found that the number of cases reported by public health was not as high as the previous wave, the number of hospitalizations did not go up that much, but there was a lot of infection … So we expect to see that there have been a very high number of cases of COVID in the population” .