New immune-evasive Omicron strains are coming. Is Canada ready?

This is an excerpt from Second Opinion, a weekly analysis of health and medical science news. If you haven't subscribed yet, you can do that by clicking here.

• New Omicron subvariants that can evade immunity better than previous strains are being detected in more countries around the world — including Canada.

• These subvariants are emerging at a time when Canada's health-care system is already under strain as flu season is fast approaching. 

• Updated COVID-19 vaccines are our best line of defence — but uptake is lagging. 

Canada is heading into a potentially brutal winter as COVID-19 hospitalizations rise, Omicron continues to rapidly mutate and booster uptake remains stagnant — all at a time when flu season is returning and the health-care system is already under intense pressure.

COVID-related hospitalizations are currently higher than any previous fall in the pandemic, nearly double last October and almost four times more than in 2020. 

And new Omicron subvariants that have been shown to better evade immunity and potentially drive new COVID waves are gaining ground, with more than 300 Omicron subvariants being tracked by the World Health Organization worldwide.​​

"All of the subvariants of Omicron are showing increased transmissibility and properties of immune escape," the WHO's COVID-19 technical lead Dr. Maria Van Kerkhove said during a news conference Thursday, adding that subvariants XBB and BQ.1.1 have shown "significant immune evasion."

"This is of concern for us because we need to ensure that the vaccines which are in use worldwide remain effective at preventing severe disease and death," she said. 

"We don't see a change in severity [with XBB and BQ.1.1], but it's very early and we have very limited data to actually assess this." 

Some of these subvariants are already being detected in countries like Singapore, India, Denmark, Australia, Indonesia, the U.S. and Canada — with BQ.1.1, BQ.1, BA.2.75.2 and XBB together making up more than 10 per cent of recent virus samples sequenced globally.

These Omicron subvariants have key mutations on their spike proteins that allow them to more easily evade the first line of defence for our immune system and enter our cells, allowing them to get around immunity from vaccination and prior infection.

"It's like a whole bunch of horses in the race at the moment and they've each gathered these different mutations," said Sally Otto, a University of British Columbia evolutionary biologist and virus modelling expert at the Coronavirus Variants Rapid Response Network.

"That means it's playing a different game, it's evolving in different ways and that is to masquerade from our immune system."

Canada preparing for 'worst case scenario'

Whether or not one or more of these Omicron subvariants will drive another wave in Canada or globally remains to be seen, but the speed with which they are being detected in other countries is cause for growing concern among experts tracking the virus.

Eric Arts, a Canada Research Chair in Viral Control and an immunology professor at Western University involved with Ontario's wastewater surveillance program, said BA.2.75.2 and BQ.1.1 have been detected in Canada but haven't taken off, while XBB is one to watch.

"XBB doesn't really care about your existing immune system as much as the other strains and so it's a pretty significant immune escape," he said, adding that Singapore is currently in an XBB-driven wave driving hospitalizations up despite very high vaccination rates. 

"The stress on the health-care system potentially with XBB from what we're seeing with Singapore right now is scary." 

Andrew Croxford, an immunologist based in Zurich, said subvariants like BQ.1.1 and XBB are being watched closely because they are "displaying potential to generate waves of infection," but they are not likely to threaten our protection against severe illness.

"They will encounter an ever-increasing wall of hybrid immunity in most countries, reducing the potential amplitude. I don't see any 'back to square one' variants in the current crop under surveillance," he said.

"I anticipate protection from severe disease to be largely maintained, with the potential exceptions of the severely immunocompromised and most frail."

The latest national immunity data from the federal government's COVID-19 Immunity Task Force (CITF) shows that while an estimated 62.5 per cent of the population has had COVID up until the end of August, there are still millions of mostly older Canadians who haven't.

The Public Health Agency of Canada said in a statement to CBC News that approximately four per cent of cases detected in Canada are BQ.1.1, three per cent are BA.2.75.2 and less than one per cent are XBB — but the reporting of virus sequence samples is weeks behind in Canada.

Canada's chief public health officer said Tuesday she is preparing for the possibility of a variant emerging in Canada that could have "very distinct immune escape," one that vaccines or treatments don't work against and can evade protection against severe illness. 

"That's one of the worst case scenarios," Dr. Theresa Tam said during an appearance before MPs on the Commons health committee. "We haven't detected one of those yet, but we need to be prepared for the potential." 

'Sleepwalking on a tightrope'

Prime Minister Justin Trudeau this week urged Canadians to get both their flu shots and COVID-19 boosters as soon as possible, in order to avoid the need for further precautions and alleviate pressure on the health-care system this fall and winter.

"If we are able to get a high enough level of vaccination, we reduce the danger of having to take other health measures to make sure that we're all safe and not overloading our hospitals," Trudeau said at an announcement in Kanata, Ont., on Monday.

But Canadians are lagging on boosters, with just 18 per cent of the population opting for a shot in the past six months and just over 50 per cent getting any booster at all — even with updated bivalent vaccines available that target Omicron and the dominant BA.4 and BA.5 strains.

"We're sleepwalking on a tightrope these days," said Dr. David Naylor, who led the federal inquiry into Canada's national response to the 2003 SARS epidemic and now co-chairs the federal government's COVID-19 Immunity Task Force. 

"There were high hopes that the availability of the new bivalent boosters would strongly motivate those who have not had a third shot. That hasn't materialized, and it's cause for concern — especially if Omicron were ever to mutate towards greater immune evasiveness and increased virulence." 

Naylor said if a variant that carries significant risk of severe outcomes takes off and begins to overload our precarious health-care systems, the failure to impose selective mask mandates would be a major dereliction of public health and political leadership.

Ontario's Chief Medical Officer of Health Dr. Kieran Moore said last week that he would recommend the return of mask mandates if the province's health care system becomes too strained — just as Ontario reported the single highest weekly death count since early May. 

"We don't have enough people taking up the vaccine, most people don't want to wear masks anymore — the circumstances exist that are ripe for an overrun of our health-care system," said Arts, at the University of Western.

"I don't know what the magic answer is except for mandates and people don't want mandates so I think we're in for a long winter."

Vaccines best protection against future surge

But despite a recent lack of urgency from the public to get vaccinated and mixed messaging from public health officials to encourage increased uptake, the time to prepare for COVID and flu season is now — and vaccines are still our best line of defence.

The National Advisory Committee on Immunization (NACI) recommends most Canadian adults should be waiting up to six months or so before getting another shot, or around three months in situations where the risk of serious illness is higher.  

"No matter how many doses you've had previously, as long as it's been at least three months from your last dose and at least a month or so from a known infection, you should be getting your bivalent booster now," B.C. Provincial Health Officer Dr. Bonnie Henry told CBC News in a phone interview. 

"Getting a booster dose now is really, really important for these next few months." 

Dr. Allison McGeer, a medical microbiologist and infectious disease specialist at Toronto's Mount Sinai Hospital, said the lack of booster uptake in Canada has been "worrying" so far, which she attributes to confusion over messaging around waiting three or six months. 

"Enough people aren't going to hit their six months until the end of November and December, when we might be into the wave already in a significant way. Now would be a really good time for us to get past the six month rule," she said. 

"You know having recently had a COVID vaccine reduces your risk of illness, long COVID, serious illness and death. Why would you want to wait?" 

Henry, who also chairs the Council of Chief Medical Officers of Health, said she's worried Canada's health-care system could be under more pressure in the coming months — not only because of COVID hospitalizations, but also flu and health-care workers getting sick.

"That's why it's so important for all of us to use all of our tools like being away from others if we're sick ourselves and getting the vaccines," she said. "That's our number one thing we can do."