After more than three years of COVID-19, most people in Canada have developed immunity against the virus through a mix of infection and vaccination, data shows.
By March 2023, more than 75 per cent of the population had immunity because of a COVID-19 infection, according to a study published in the Canadian Medical Association Journal (CMAJ) Monday.
Researchers at the COVID-19 Immunity Task Force looked at blood samples of thousands of Canadians of all ages collected between March 2020 and March 2023 and found that the Omicron variant led to a rapid rise in infection-induced antibodies last year.
During the Omicron waves, the rates of infection-acquired immunity appeared to be highest among younger Canadians, the CMAJ research showed.
“Data up to March 2023 indicate that most people in Canada had acquired antibodies against SARS-CoV-2 through natural infection and vaccination,” the authors said in the peer-reviewed study.
The research sheds new light on the impact of the highly transmissible Omicron variant — which was first detected in Canada in December 2021 — which caused many Canadians to get infected for the first time with COVID-19.
The study also said most people in the country had been vaccinated by the time the Omicron variant surged in Canada – and that coupled with an uptick in cases ushered in “an era of hybrid immunity” that potentially could protect against infection for months.
Despite the high vaccine coverage, the hybrid immunity from vaccines and previous infections was not enough to slow the spread of Omicron, the CMAJ study stated.
“I think the big message out of this is that vaccination is hugely important still,” said Gerald Evans, an infectious diseases specialist at Queen’s University in Kingston, Ont.
“We had vaccine immunity prior to the Omicron surge in … most of the people who were at high risk, of course, which are older people and people with underlying conditions,” he told Global News.
Canada’s National Advisory Committee on Immunization (NACI) released fall booster guidance last month, recommending a dose of the new formulation of the COVID-19 vaccine for the authorized age groups.
NACI says all Canadians aged five years and up should get a COVID-19 booster in the fall if it has been at least six months since their last vaccine dose or infection, whichever is later.
Evans estimates about one in four Canadians likely have still not had COVID-19, but they’re probably protected by vaccination, he said.
Hybrid immunity – from both vaccination and prior infection – does confer some added benefits, Evans said, especially as new variants emerge.
“We’re not seeing anywhere near the number of COVID cases we saw even last summer when we actually had a bit of a summer surge,” he said.
“So this is telling us that right now, at least, this hybrid immunity that we have is doing a good job at protecting us a lot.”
However, the authors of the CMAJ study did warn about the potential for waning antibody levels and new variants that may escape immunity.
A fast-spreading COVID-19 subvariant of Omicron is now circulating in Canada and globally.
The World Health Organization (WHO) has classified EG.5 as a “variant of interest.”
Experts in Canada are warning about another surge in COVID-19 cases in the fall as schools reopen, the weather cools and people spend more time indoors.
“We will see a rise in cases, perhaps a surge, but I don’t think we’re going to see a wave of cases, at least at this point, unless something changes,” Evans said.