3 key factors in how Canada will fare during the 4th wave of COVID-19

It's tough â€" even impossible â€" to predict exactly how Canada will fare in the fourth wave of the COVID-19 pandemic. And looking for clues from other countries only gets you so far.

Some regions are being overwhelmed, yet again, by this virus; others are avoiding catastrophe largely thanks to high vaccine uptake and other precautions. Widely different policy decisions and levels of restrictions also mean there's no one-size-fits-all outcome.

So what will determine Canada's experience in the months ahead?

Multiple experts told CBC News that there are a few key factors in how the pandemic will play out as the delta variant continues spreading.

According to Matthew Miller, an associate professor of infectious diseases and immunology at McMaster University in Hamilton, there's also good reason to hope that Canada might fare even better than many other countries with similar public health measures, thanks to our high vaccination rate and unique approach to immunizing residents.

"Vaccinated people in Canada are going to be much better off than vaccinated people almost anywhere else because of a reliance on mRNA, mixed-vaccine schedules and extended intervals," he said.

"Obviously, though, as infectious disease experts and public health experts have rightly pointed out, a mixture of measures is still going to be required to control the pandemic effectively â€" and those are going to have profound influences on how we as a population experience the fourth wave."

WATCH | Vaccine expert weighs in on how Canada could fare in the 4th wave: Vaccine expert weighs in on how Canada could fare in the 4th wave16 hours agoMatthew Miller, an associate professor at McMaster University in Hamilton, explains some of the key factors at play in how Canada could fare in the fourth wave of the COVID-19 pandemic. 1:11 1. Vaccine uptake

Despite a sluggish start, Canada quickly became one of the most heavily vaccinated countries in the world against COVID-19.

Roughly 63 per cent of the total population is now fully vaccinated, and the number is slowly ticking higher.

While millions of people across the country remain unprotected, virologist Alyson Kelvin said Canada's relatively high rate of immunization bodes well.

"We have fairly good coverage," said Kelvin, who works with the Vaccine and Infectious Disease Organization (VIDO) at the University of Saskatchewan in Saskatoon.

"And the stats have come out that it seems we have better coverage compared to other countries â€" that's going to be our biggest source of protection, that we were able to vaccinate so many people and, again, stop that chain of transmission of the virus."

While high vaccination rates haven't entirely blunted COVID-19 infections in other areas of the world, they have noticeably reduced cases of serious illness compared with earlier surges of the coronavirus.

People stroll through Montreal in late August. 'We're in a different landscape right now where a lot of public health measures have been lifted,' said virologist Alyson Kelvin, who works with the Vaccine and Infectious Disease Organization (VIDO) at the University of Saskatchewan in Saskatoon. (CBC/Radio-Canada)

In Spain, which has about a 66 per cent vaccination rate â€" a little higher than in Canada â€" the country's latest wave of infections shot up the virus's daily death toll, but nowhere near levels seen in earlier waves.

The heavily vaccinated U.K. also experienced a surge, then a dip before seeing another increase in cases this summer, but throughout it all, rates of hospitalization and death were far lower than earlier in the pandemic.

And in Iceland, where roughly 72 per cent of the total population is fully vaccinated, the rates of COVID-19 hospitalization remained low even as infections went up â€" and the country hasn't recorded a single virus death since May.

McMaster University's Miller said it's crucial for Canada to get its vaccine uptake as high as possible by improving access, encouraging those who are still hesitant and even mandating vaccines in certain settings â€" particularly when it comes to persuading younger age groups.

"A little bit of pain with vaccine passports to do certain things that that demographic likes to do â€" go to clubs, eat indoors at restaurants â€" that'll be enough to push those people to get vaccinated," he said.

"That's really where a vaccine mandate will make the biggest difference, I think, is in that younger group that are lagging a little bit behind right now."

Already, there's a patchwork of vaccination policies and mandates coming into force in health-care institutions, concert venues, universities and various levels of government across the country â€" but it's not yet clear how much those efforts will increase uptake.

WATCH | Vaccination key to avoiding the worst from delta variant, experts say: Vaccination key to avoiding the worst from delta variant, experts say4 days agoWith the delta coronavirus variant making up more than 80 per cent of cases in Canada, experts say most people will encounter it. Getting a COVID-19 vaccine will prevent the worst outcomes. Correction: At 1:30 in this story, Dr. Mike Nayak is incorrectly identified as Mark Nayak. 2:44 2. Delaying, mixing different vaccines

Canada's vaccination strategy was quite unorthodox in several ways, giving Canadians the ability to mix between different forms of vaccine technologies and space out doses.

Born out of necessity during a shortage of supplies, the approach stirred up controversy and even derailed some Canadians' travel plans after some countries and cruise lines refused to accept people who received two different shots.

But Miller â€" who is affiliated with Canada's National Advisory Committee on Immunization but isn't speaking on the advisory body's behalf â€" said the recommendations were rooted in decades of vaccine science and could have a "profound influence on the longevity of the immune response."

The unique road Canada took â€" allowing people to get second doses well beyond manufacturing guidelines, to a maximum of four months â€" is now likely a better bet than sticking to the speedy timelines used in clinical trials, he said.

"We know mixing and matching, we know that delayed prime-boost schedules really do give a better overall protective effect from vaccination," Kelvin said, though she noted that more research is still needed.

Manitobans enjoy outdoor yoga with puppies at the Bronx Park Community Centre in Winnipeg in late August. More people are socializing again, with looser restrictions now in place in much of the country, even as Canada is dealing with the early days of a fourth wave of COVID-19. (Tyson Koschik/CBC)

Emerging studies, however, are starting to back up the early recommendations around mixing different vaccine technologies, with a focus on using the highly effective mRNA-based options, said Dr. Allison McGeer, a professor at the University of Toronto and an infectious disease physician at Mount Sinai Hospital in Toronto.

"From what we know about T-cell immunity and antibodies, probably the best two doses to have are AstraZeneca followed by one of the mRNA vaccines," she said, referring to the Pfizer-BioNTech and Moderna vaccines. "So that was a really good choice for Canada, I think, to make that recommendation â€" and almost certainly better than two doses of AstraZeneca."

McGeer said while Canada's unique approach helped to get more shots in arms, she isn't convinced it would necessarily make much of a difference in how the country fares in the fourth wave.

And Miller acknowledged that not every Canadian got their shot in the same manner, making it hard to know how the country's strategies will play out.

"One complexity, of course, is that on the bookends of our vaccine rollout, there are exceptions, right?" he said. "So many health-care providers and long-term care residents got their vaccine in the recommended interval."

WATCH | How convenient COVID-19 vaccine clinics help convince some to get the shot: How convenient COVID-19 vaccine clinics help convince some to get the shot15 days agoAs health officials work to get more people vaccinated against COVID-19, there’s hope that convenient pop-up clinics could help some decide to get the shot. 2:01 3. Public health measures and restrictions

To buy time while more Canadians get vaccinated, multiple experts point to the need for certain public health measures to keep case growth at bay â€" not necessarily a full lockdown but some level of restrictions.

That means maintaining the basic day-to-day precautions Canadians now know well: mask-wearing, physical distancing, avoiding large gatherings and crowded settings.

"We really need to think about our current situation and how having layers of protective measures really keeps everybody safe," Kelvin said.

"We're in a different landscape right now where a lot of public health measures have been lifted."

Bringing back certain precautions will be particularly crucial as millions of unvaccinated children return to school this fall, according to Miller, who also said that's the issue bringing the most uncertainty to the months ahead.

Both vaccines and some level of restrictions should be used in tandem to put Canada in the best position as delta-driven cases keep rising, several experts agreed.

"If we are really concerned about protecting vulnerable populations â€" people in long-term care facilities, those people who are immunocompromised, such as transplantation recipients â€" these multiple layers will help protect them," Kelvin said.

"So it's all of our jobs to take part in this."

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