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A COVID-19 vaccination site in Montreal on Jan. 8.Graham Hughes/The Canadian Press

As cold and flu season approaches, Canada may be unprepared to cope with new COVID-19 variants that are adept at evading immunity from vaccines and prior infections, health experts say.

The Omicron variant first arrived in the country nearly a year ago. Within a matter of weeks, it was responsible for the vast majority of COVID-19 infections here. But now the situation has changed: In recent months, a number of Omicron subvariants have emerged, one after the other. More are likely on the way.

The new subvariants have mutations on their spike proteins, which are the parts of the virus that allow it to enter human cells. These altered proteins enable the subvariants to infect even people who are vaccinated, or who have already recovered from bouts of COVID-19.

People who are up to date on their COVID-19 vaccinations still have high levels of protection against severe illness, but uptake of booster doses has been sluggish, meaning many Canadians are still vulnerable. In the past six months, only about 18 per cent of people in Canada aged five or older have completed their initial vaccine series or received boosters.

“When there’s broad population immunity, it puts pressure on the virus to find advantages, such as escaping our existing immunity from infection or from vaccines,” Theresa Tam, Canada’s chief public health officer, told the House of Commons health committee this week. “This broad range of the descendants of Omicron are now being carefully monitored.”

Sarah Otto, a theoretical biologist at the University of British Columbia who has been following the evolution of the virus, said the variants emerging now are gaining ground by taking advantage of this ability to cut through prior immunity. New bivalent vaccines, which target Omicron specifically, are meant to mitigate this. But they cannot completely eliminate the threat.

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According to the most recent data available from the Public Health Agency of Canada, the Omicron subvariant known as BA. 5 was responsible for 88 per cent of COVID-19 infections as of Sept. 25, followed by BA. 4, at about 11 per cent. BA. 2 accounted for the rest.

Some of the other Omicron subvariants making headlines around the world, such as XBB, BQ. 1 and BQ. 1.1, haven’t yet become prevalent in Canada.

The XBB subvariant has caused an upsurge in COVID-19 cases in Singapore. But it appears that countries that had major Omicron-fuelled waves in early 2022, including Canada, have some immunity against XBB.

“That wave actually, we hypothesize, may be protecting us against some variants,” said Fiona Brinkman, a professor at Simon Fraser University who specializes in infectious disease genomics and is a member of the Coronavirus Variants Rapid Response Network.

Dr. Tam told the Commons health committee this week that another variant of concern, BA. 2.75, had stalled at about 1 per cent of the COVID-19 cases sequenced in Canada as of mid-September.

It’s a different story with BQ. 1 and BQ. 1.1, which appear to have “very high potential to spread well, and spread very well compared to XBB,” Dr. Brinkman said.

The BQ. 1 subvariants still represent less than 1 per cent of COVID-19 samples sequenced here, according to Dr. Tam. But, considering the rapid growth of those versions of the virus in some European countries, officials here are watching them closely.

A worrying aspect of the BQ. 1 and BQ. 1.1 subvariants is that they don’t respond to monoclonal antibody therapies, which means Paxlovid, the antiviral medication developed by Pfizer, will be the only pharmaceutical treatment option for many high-risk people, Dr. Brinkman said. But some patients can’t take Paxlovid because it interacts with dozens of common medicines.

While many people may experience only mild symptoms as a result of these new variants, some, including seniors or people with compromised immune systems, remain vulnerable. And with large numbers of Canadians behind on their COVID-19 vaccines, the new versions of the virus could easily spread to those populations.

On top of that, hospitals in many parts of the country are over capacity and struggling to care for patients. All of these factors could make for a very difficult cold and flu season.

Experts say it’s important for people to get vaccinated against COVID-19 when they are eligible, despite pandemic fatigue.

“We need to keep those levels of antibody up in our immune systems to maintain that protection,” said Manish Sadarangani, a pediatrics professor at the University of British Columbia and director of the Vaccine Evaluation Center.

With a report from Ivan Semeniuk

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