Almost half of Canadians may have caught COVID

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Canada's COVID-19 immunity landscape has completely transformed since the emergence of Omicron — with new estimates suggesting that almost half of the population has been infected.

Researchers in B.C. analyzed thousands of blood samples in the Lower Mainland throughout the pandemic to track antibody levels in the general population, and found a massive shift in the level of infection in the past few months.

The B.C. data, provided in advance to CBC News, found close to 40 per cent of the population had antibodies from a previous infection in March, up from around 10 per cent in October. That number is even higher in children under 10, with nearly two-thirds now showing evidence of prior infection.

"Think about that — two out of three children," said Dr. Danuta Skowronski, a vaccine effectiveness expert and epidemiology lead at the British Columbia Centre for Disease Control who led the research.

"Wow, something really dramatically changed and I think we know the name of that change … it's Omicron." 

Skowronski said close to 60 per cent of those aged 10 to 40 also had antibodies from prior infection, and just under 50 per cent of those aged 40 to 60. There were slightly lower levels in those aged 60 to 80 — possibly because they were less socially engaged and vaccinated earlier.

The data also suggests almost 90 per cent of the population has had their immune system primed against the virus in some way — either through vaccination, prior infection or both.

Skowronski, whose research laid the groundwork for the decision to delay second doses in Canada, said we are in a "vastly different context" now than at the start of the pandemic, when we had basically "total population naivety" to the virus.

"It's about one in two, almost, of our population that have had evidence of infection," she said. 

And while the data provides a useful snapshot to estimate the level of infection in the community, she said it doesn't directly translate to exact population immunity levels. 

"We cannot say that this is an indication of protection or being exempt from future infections, especially when new variants arise. But a primed person is immunologically a prepared person."

While the data is preliminary and has yet to be peer reviewed or published, it is in line with emerging data from other provinces, like Ontario, where official estimates now show as much as 40 per cent of the population was infected with COVID-19 since December alone.

"We have had millions of infections in the last few months, most of them undocumented," said Dr. David Naylor, who led the federal inquiry into the 2003 SARS epidemic and now co-chairs the federal government's COVID-19 immunity task force.