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Tests for COVID-19 antibodies in donated blood indicate that around 73 per cent of Canadians have contracted the virus at some point. The numbers were much lower in seniors and higher in 17-24 year olds.Rick West/The Associated Press

Almost three-quarters of Canadians have now had COVID-19, although far fewer seniors have caught the coronavirus, tests of blood donations show.

Tests for COVID-19 antibodies in donated blood indicate that only around 60 per cent of seniors have contracted the virus, compared to 88 per cent of those between 17 and 24 years of age.

Sheila O’Brien, associate director of epidemiology and surveillance at Canadian Blood Services, said the discrepancy in infection rates may reflect behaviour and lifestyles.

Many older people work from home, may be retired or may be more cautious about mixing in large groups. Seniors are also more inclined to have regular booster shots and to wear masks.

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Younger people, by contrast, are more likely to interact with many other people, including at school and college, and through sport, as well as in restaurants and bars.

The government’s COVID-19 Immunity Task Force presented the new data to Chief Public Health Officer Theresa Tam on Thursday.

Tests from Canadians who give blood – reflecting a broad range of ages and socio-economic groups – showed that around 73 per cent of Canadians have now contracted the virus. Most have caught the highly contagious but less virulent Omicron variant.

Before Omicron took hold in January, 2022, only around 5 per cent of Canadians had contracted the virus, Ms. O’Brien said.

More than 50,000 Canadians have died after catching COVID-19, the Public Health Agency of Canada confirmed this week.

On Friday, a World Health Organization committee will meet to discuss whether the pandemic should still be classed as a global public-health emergency.

Among racialized Canadians and Indigenous people, the rates of infection in Canada are higher than the general population, with 81 per cent having contracted COVID-19 overall, the blood samples show.

Public Health has said higher rates of infection among racialized groups reflect “existing health inequalities” and social and economic factors, such as income, education, employment and housing.

Canadian Blood Services tests blood taken from donors from every province except Quebec for antibodies from a previous infection.

The data helps inform the COVID-19 Immunity Task Force, which advises Public Health and other policy-makers, about infection rates.

The figures, from last month, showed that 80 per cent of 25 to 39 year olds had the virus, with 74 per cent of 40 to 59 year olds.

David Buckeridge, scientific lead for data management and analysis on the task force, said the findings suggest levels of infection slowed toward the end of 2022. But he warned it would be difficult to predict if this trend will continue as the virus is mutating.

He said evidence suggests that rates of infection are rising more rapidly among the over-60s who are less likely to have already had COVID-19.

“Because we are seeing higher levels of prior infection in younger folks, and lower in older adults, that means they don’t have that additional immunity boost that may have come from a prior infection,” he said.

But he said older Canadians “have relatively high vaccine coverage,” so they may not “necessarily have poor outcomes” and get very sick if infected.