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OTTAWA — Manitoba is undertaking a blood-sample survey of how many people have recovered from COVID-19, after a study of blood donors suggested nearly seven times the reported number of infections.

Dr. Catherine Hankins said blood-donation data from November show just how badly COVID-19 hit Manitoba in the pandemic’s second wave.

"They do reveal that what was going on in November was also going on asymptomatically," said Hankins, a McGill University public health professor who co-chairs the national COVID-19 immunity task force.

Her team helped analyze donations Canada Blood Services collected outside of Quebec in November, and found 8.56 per cent of the 380 Manitoba samples contained antibodies to COVID-19, compared to 1.51 per cent nationally.

If the studied samples proportionately reflect the entire province, it would mean the number of Manitobans who had caught COVID-19 by Nov. 30, 2020, would have been seven times the officially reported 16,513 infections — and four times the cumulative infections reported up to Jan. 31.

Manitoba’s rate of antibodies was more than double second-place Saskatchewan — although Quebec has likely had the highest infection rate in Canada, and uses a separate blood-donation system.

Yet, Dr. Jazz Atwal, acting deputy chief provincial public health officer, said the blood-donation numbers are likely an overestimate of what’s happening in the community.

"In Manitoba, there are certain populations who have higher impacts related to COVID-19 infections, and those same groups of individuals are very good at donating blood," Atwal said Tuesday.

Hankins agreed, saying blood donors across Canada tend to be healthy, urban volunteers, who are 17 or older.

She said multiple provinces are screening samples they collect for various blood tests to surveil how widespread COVID-19 antibodies are in the population, which is a more randomized sample.

Atwal did not offer specifics, but confirmed some sort of study is underway.

"We have work being done to look at a better random sample for Manitoba as well to look at blood samples throughout the province and not just with specific populations," he said.

"It gives us a much better sampling of the population, which will provide us a better much better indication of seroprevalence in the province."

A provincial spokeswoman said Canada Blood Services tends to gather donations from southern Manitoba, while "the province takes a broader approach that tries to cover all populations and age groups" and is testing samples to see if the numbers match the CBS results.

In any case, the November blood-donation analysis found 5.09 per cent of the 288 analyzed Winnipeg samples contained antibodies, by far the highest among six major Canadian cities.

It also found antibodies in a whopping 27.5 per cent of 38 samples collected in the region spanning Thompson, Island Lake and Norway House, known as "north-central Manitoba."

Hankins said both blood donations and samples from blood tests can help suggest how widely COVID-19 has spread, and how many people were infected without even knowing it. She’s hoping provinces share the data they generate from their own blood-sample surveillance.

She also noted the blood-donation analysis shows a drop in antibodies in as little as four months.

The November survey included samples from 82 blood donors who had antibodies detected in samples collected between May and July. Only 77 per cent still had antibodies during the November study.

Hankins said it shows a drop in the strength of the antibodies but people might still have enough immunity to ward off a COVID-19 infection, even when their antibodies drop below the sensitivity of the test that was used.

Similarly, the high number of Manitoba cases could be due to the rate of recent recoveries, which would produce a high number of antibodies that would be picked up in testing.

Meanwhile, Hankins’ team is also rolling out testing kits to a sample of 48,000 Canadians that Statistics Canada has selected to equally represent different regions, genders and ages, including 3,634 Manitobans.

The first round of test kits, which require a pinprick and drops of blood on a special paper card, only had a response rate of roughly 25 per cent.

— with files from Danielle Da Silva