Almost half of Canadians may have caught COVID


This is an excerpt from Second Opinion, a weekly health and medical science newsletter. If you are not yet a subscriber, you can do so by clicking on here.


The Canadian COVID-19 immunity landscape has completely transformed since the emergence of Omicron – with new estimates suggesting almost half the population has been infected.

British Columbia researchers analyzed thousands of blood samples in the Lower Mainland throughout the pandemic to track antibody levels in the general population and found a massive change in the level of infection over the course of the pandemic. of the last few months.

British Columbia data, provided in advance to CBC News, found nearly 40% of the population had antibodies from a previous infection in March, up from about 10% in October. This number is even higher in children under the age of 10, with nearly two-thirds now showing signs of previous infection.

“Think about that – two out of three children,” said Dr. Danuta Skowronski, a vaccine effectiveness expert and epidemiology manager at the British Columbia Center for Disease Control who led the research.

“Wow, something really drastically changed and I think we know the name of that change…it’s Omicron.”

People are shown in downtown Vancouver last month. New data from British Columbia has shown a major increase in antibody levels in the general population in recent months as the country grapples with the Omicron variant of COVID-19. (Ben Nelms/CBC)

Nearly 90% vaccinated, infected or both

Skowronski said almost 60% of people aged 10 to 40 also had antibodies from a previous infection, and just under 50% of those aged 40 to 60. There were slightly lower levels in people aged 60 to 80 – possibly because they were less socially engaged and vaccinated earlier.

The data also suggests that almost 90% of the population has had their immune systems primed against the virus in some way – either through vaccination, previous infection, or both.

Skowronski, whose research laid the foundation for the decision to delay second doses in Canada, said we are now in a “very different context” than at the start of the pandemic, when we essentially had “the complete naivety of the population” to the virus.

“It’s about one in two, almost, of our population that has had evidence of infection,” she said.

And while the data provides a useful snapshot for estimating the level of infection in the community, she said it does not directly translate to exact levels of population immunity.

“We can’t say that’s an indication of protection or of being free from future infections, especially when new variants emerge. But a primed person is immunologically a primed person.”

Although the data is preliminary and has not yet been peer-reviewed or published, it aligns with emerging data from other provinces, such as Ontario, where official estimates now show as many as 40% of the population was infected with COVID-19 since December only.

“We’ve had millions of infections over the past few months, most of them undocumented,” said Dr David Naylor, who led the federal investigation into the 2003 SARS outbreak and now co-chairs the task force. on federal government COVID-19 immunity.

“I wouldn’t be surprised if the actual number is over 10 million nationally by the end of wave six.”

WATCH | Children’s hospitals hard hit by the 6th wave of COVID-19 in Canada:

Children’s hospitals under pressure in the 6th wave of COVID-19

The sixth pandemic wave is causing high patient volumes and staffing shortages at a number of children’s hospitals across Canada, worrying parents and medical experts about the spread of COVID-19 among children . 2:06

Canada has become a variant magnet

Canada’s COVID-19 immunity landscape is one of the most complex in the world due to our high vaccination rates, widespread transmission, delayed and mixed doses, and the fact that we have been a magnet for variants – often with several circulating at the same time.

But does the protection we’ve gained from vaccines, previous infection and combined hybrid immunity mean the worst is behind us? Or could waning immunity to infection, the spread of new variants, or another pandemic curve threaten another surge in the future?

“If there is a future variant that has infectious advantages over Omicron, we can expect it to arrive and spread here,” Naylor said. “It’s been clear from the past two years. SARS-CoV-2 is going pretty much everywhere at a rapid pace.”



Canada’s bold decision to delay and to mix together doses of COVID-19 vaccines led to strong protection against hospitalization and death, but the emergence of Omicron and its subvariants made them less protective against infection than previous viral strains.

A new Canadian study on pre-publicationwhich has not yet been peer-reviewed, found that the efficacy of just two doses of Pfizer-BioNTech, Moderna and AstraZeneca-Oxford vaccines was “excellent” against severe consequences of COVID-19 through September 2021 .

This research follows another new study co-authored by Skowronskiand published in Clinical Infectious Diseases, which showed two doses of mRNA vaccines or AstraZeneca “provided substantial and long-lasting protection” against Delta’s hospitalization, through November 2021.

While vaccine efficacy against severe consequences held up well, two-dose protection against Omicron infection dropped dramatically in December, falling to just 36%, according to a Pre-printed study in Ontariowith boosters bringing it to 61%.

This major blow to the immunity of our population highlighted the need for boosters and left us very susceptible to the fifth and sixth waves powered by Omicron which have since torn the population apart.

“Complex” immune landscapes

Tulio de Oliveira, director of South Africa’s Center for Epidemic Response and Innovation, which led the research team that identified the BA.4 and BA.5 subvariants, said countries like Canada have now “very complex” immune landscapes as a result of Omicron.

“That means what one country sees with a variant and a sub-variant may be slightly different from what other countries see,” he told CBC News in a phone interview.

“But if population immunity is increased, particularly through vaccination and reinforcement, that should still bode very well not only against Omicron, but potentially against any new variants that may emerge.”

The National Advisory Committee on Immunization (NACI) of Canada strongly recommends stimulate all high-risk adults and children earlier this month, and de Oliveira said the most effective way to boost a population is before a new wave of infection begins.

WATCH | Canadians urged to get COVID-19 reminders to blunt the 6th wave:

Canadians urged to receive COVID-19 booster shots to blunt 6th wave

All signs point to Canada going through a sixth pandemic wave, confirms Dr. Theresa Tam. His message to Canadians: Wear a mask and get boosted if you’re eligible. 2:00

“That’s what countries should focus on,” he said. “When the infection is low, it’s a great idea to launch a booster campaign for people who have been fully vaccinated, or vaccinated and infected, because then the next wave that arrives will be much less deadly.”

Naylor said our past immunity to infections, combined with current vaccination coverage, the continued rollout of boosters, extra doses for children and the “intelligent use” of fourth doses among eligible Canadians should provide a ” immune wall strong enough for the summer”.

“It is prudent to remember, however, that no one predicted Omicron,” he said. “And so that wall of immunity can still be broken.”

“Running out of territory” with current vaccines

While a high rate of vaccination and previous infection in Canada does not guarantee that the worst is behind us, it is clear that it will continue to reduce the likelihood of serious consequences from COVID-19 for the vast majority of Canadians. .

But as the virus continues to evolve into new variants that are light years away from the original strain that vaccines are targeted at, the drive to update formulations to target Omicron and other variants is a priority.

“We need broader vaccine coverage. Much to my frustration, we’re still targeting a strain that’s been long gone,” said University of Arizona immunologist and professor Deepta Bhattacharya.

“I understand the practical reality is that these are the tools we have on hand right now, but we’re definitely out of territory in terms of what we can expect from these vaccines, given how different Omicron is from what vaccines are aimed against.”

Modern announced new findings this week showing that a booster shot designed to target both the beta variant and the original viral strain generated a better immune response against several other variants, including Omicron.

While this exact formulation will likely never see the light of day, it bodes well for the possibility of tailoring future mRNA injections to target multiple variants. But until we have updated vaccines, immunity from previous infection can fill the void.

WATCH | Moderna’s vaccine targeting COVID-19 variants shows promise:

Moderna’s vaccine targeting COVID-19 variants shows promise

A new version of Moderna’s COVID-19 vaccine appears to offer protection “against all variants of concern,” according to preliminary results released by the company. It plans to offer a vaccine that will target both the original strain and the Omicron variant as early as this fall. 2:00

“Given the vaccine mismatches with Omicron, it is almost certain that prior infection of Omicron with BA.1 would confer more protection against Omicron sublines, such as BA.2,” Bhattacharya said.

“So people who have recovered from BA.1 are almost certainly in better shape to cope with BA.2 than someone who just had a few shots of the vaccine in the past,” he said.

Skowronski said Canadians are more immunologically prepared against COVID-19 than ever before. And if Omicron continues to develop new variants when almost half of us have been infected with them, there will be “cross-protection”.

“We can’t predict what later variants might be. They will likely be related to evolution, but maybe not to Omicron,” she said, adding that COVID-19 vaccines might need to be updated. updated regularly by a team of international experts, much like flu vaccines are.

“The question is, to what?”