Chief Public Health Officer of Canada Dr. Theresa Tam speaks during a news conference on the COVID-19 pandemic in Ottawa on Tuesday, Dec. 22, 2020. As several countries report an uptick in COVID-19 cases that has been partly blamed on a more contagious version of the Omicron variant, the question becomes whether Canada's next wave will be a surge or a ripple. THE CANADIAN PRESS/Justin Tang

As several countries report an uptick in COVID-19 cases partly blamed on a more contagious version of the Omicron variant, the question becomes whether Canada's next wave will be a surge or a ripple.

The confluence of easing COVID-19 protocols and the rise of BA.2, a sublineage of the Omicron variant, is complicating the epidemiological forecast for spring, experts say.

While most agree that Canada's immunization rates should blunt the impacts of the so-called "stealth" subvariant, some worry that decreased public health vigilance could clear a path for BA.2 to drive up infections and hospitalizations.

Canada's chief public health officer suggested last week that the country should be shielded from the worst of the COVID-19 resurgence that's roiling regions abroad, instead predicting a spring "blip" as public health measures are lifted.

While evidence suggests that BA.2 is more transmissible than its Omicron predecessor, the subvariant is spreading at a relatively slow rate in Canada, said Dr. Theresa Tam.

It doesn't appear to to cause more severe illness than other variants, she said, but international data suggests BA.2 targets people who aren't protected by vaccination or previous exposure to the Omicron variant.

That means Canada's high immunization uptake — with 81 per cent of the population considered fully vaccinated — should keep hospitalizations at manageable levels even if cases rise, said Tam.

But Dr. Lynora Saxinger, an infectious disease specialist at the University of Alberta, warned that the risks of BA.2 could be unevenly distributed across Canada.

Omicron reinfection appears to be rare, Saxinger said, so regions that were hit hard by the BA.1 surge may fare better than those where the variant hasn't been circulating.

"I think it will be very variable between even cities, communities and provinces, and overall across the country," she said. "In places where they haven't had a lot of infection recently, I think there is a bit more risk that this highly transmissible variant could make a bigger wave."

Another factor to consider is uptake of third vaccine doses, which do a lot "heavy lifting" in protecting against severe outcomes from Omicron infection, said Saxinger. Federal numbers suggest that roughly 46 per cent of the population has received a booster shot.

What's less clear to Saxinger is whether reimposing COVID-19 rules would do much to curb BA.2's spread, noting that the subvariant has gained steam in places with strict public health measures.

"I think there's a wide playing field in between giving up, which I don't think is the right answer, and doing some sort of draconian lockdown on an early signal."

Caroline Colijn, a mathematician and epidemiologist at Simon Fraser University, isn't convinced that BA.2 will register as just a "blip" in Canada's COVID-19 trajectory.

The Canada 150 Research Chair in Mathematics for Evolution, Infection and Public Health said her modelling suggests that Canada is well positioned to weather an uptick in transmission driven by either BA.2 or relaxing COVID-19 restrictions independently, but the combination of the two could cause problems.

"We can be very resilient to a rise in transmission, and BA.2 will give us a rise in transmission. But reducing our measures and removing our protections will also give us another rise in transmission at the same time," Colijn said.

"I think we are resilient to some increase in transmission. But I think we will probably see a surge from these two increases in transmission arriving at the same time."

Of particular concern to Colijn is how BA.2 could affect those who are most vulnerable to severe COVID-19 outcomes, such as people who are older or immunocompromised.

These groups were prioritized for early boosters in many parts of the country, Colijn noted, and so the immunity provided by these doses are more likely to have waned in the months since.

As many provinces have restricted access to testing, Colijn said, we may not have the data we need to measure to increased COVID-19 transmission before hospitalizations tick up, at which point, it'll be too late to contain the situation.

"I think we should be going into this with our eyes open and watching carefully," she said.

This report by The Canadian Press was first published March 22, 2022.

News from © The Canadian Press, 2022