COVID-19 exposure has risen fastest in the West: study

Exposure to the novel coronavirus among healthy adults has grown fastest on the prairies, but herd immunity remains distant and only possible through mass vaccination, according to a national study.

Samples from 33,860 blood donations collected last October and November suggest 1.5 per cent of healthy Canadian adults have COVID -19 antibodies, indicating they've been exposed to the virus.

But in the West, those numbers are greater and have climbed faster since last spring and summer — five times higher in Manitoba and Saskatchewan, while in B.C. and Alberta, they've at least tripled.

In Alberta, that number of antibody-positive blood samples collected by Canadian Blood Services went from .48 per cent from May to July to 1.79 per cent in November.

And those numbers in Calgary and Edmonton were higher than most other larger Canadian cities with 2.22 per cent and 2.23 per cent respectively, compared to Toronto at .98 per cent.

“In Alberta, it's really reflecting what you're seeing as cases have gone up pretty dramatically,” said Dr. Catherine Hankins, co-chair of the COVID-19 Immunity Task Force.

Even so, the overall numbers remain low and point to a reality that should dispel any notion that Canada's 38 million people are on their way to so-called herd immunity.

“It tells us so many people are still vulnerable,” said Hankins.

That means Canadians must remain vigilant in their daily protective practices while hoping vaccines — facing disrupted supplies — ultimately roll out quickly and efficiently, she said.

“What these numbers also tell us is Canadians have been really good at trying to keep that down,” said Hankins, adding the arrival of new, more infectious variants of the virus have added urgency to that.

Despite a major, weeks-long delay in delivery of the Pfizer-biontech vaccine, Hankins remains optimistic the country is on the right track and should be assisted with Canada's approval of the Astrazeneca version and others.

Concerns over polls showing 20 per cent of Albertans are reluctant to receive a COVID -19 vaccine are likely overblown, said Hankins.

Many of those people will eventually receive it, she said, once they're confident in its safety.

And the high demand for the vaccine across the country bodes well for the country as a whole, said Dr. Sheila O'brien, associate director of epidemiology and surveillance at Canadian Blood Services.

“If only a small number of people don't receive it, we can come pretty close to herd immunity,” said O'brien.

The study isn't a uniform representation, with some pockets of the population more highly represented than others, she noted.

But it confirms racialized Canadians have been more exposed to the virus, said O'brien.

“Racialized Canadians are more likely to have antibodies against COVID -19 than white donors, and the disparity seems to be widening over time,” states Dr. O'brien.

A larger blood sample study to be conducted in the next few months will determine how many antibodies were acquired naturally and how many through vaccinations, said O'brien.

So far, just over 99,000 people have been inoculated against COVID-19 in Alberta, with 25 of those resulting in adverse effects, says Alberta Health.