Health·Second Opinion

4th wave of COVID-19 likely if Canada reopens too fast — and seasonal return may be inevitable

As Canada beats back its third coronavirus wave, experts warn a fourth one could strike at any time if restrictions are lifted too quickly. While there's hope that could be prevented with more vaccinations and careful reopening, seasonal COVID-19 might be here to stay.

Experts say vaccines, careful reopening could prevent dire surge, but seasonal COVID-19 might be here to stay

Post-pandemic life is getting closer in Canada, beyond lower-risk activities like patio dining seen here in Surrey, B.C., in mid-April. But experts warn fully reopening too quickly could lead to a fourth wave of COVID-19 cases. (Ben Nelms/CBC)

This is an excerpt from Second Opinion, a weekly roundup of health and medical science news emailed to subscribers every Saturday morning. If you haven't subscribed yet, you can do that by clicking here.

As Canada beats back its third coronavirus wave, experts warn a fourth one could strike at any time if restrictions are lifted too quickly — but there's hope that could be prevented with more vaccinations and careful reopening.

The potential for a fourth surge of cases comes as multiple provinces struggle to get case counts back down after the gruelling third wave started in March. 

In recent weeks, B.C. hit record-high intensive care admissions, Alberta reported the highest case rate in Canada, and Ontario has been struggling to boost hospital capacity amid an overwhelming level of COVID-19 admissions by transferring patients across the province, halting non-emergency procedures, and bringing in medical teams from the Canadian Armed Forces.

But that is starting to turn. Provincial restrictions and rising vaccination rates are bringing new cases down, and warmer weather is on the way, prompting words of caution from medical experts over reopening too fast and too soon.

Physician-epidemiologist Dr. Nitin Mohan, a public health consultant and assistant professor at Western University in London, Ont., said lifting the bulk of restrictions before Canada boosts vaccination rates and achieves high levels of protection in hot spots could derail all the recent progress and spark a fourth wave.

"This is not to fear-monger," he said. "This is very much factual, and we have evidence from previous waves."

'We need to be prudent'

Speaking of the current situation in Ontario, Dr. Peter Juni, scientific director of Ontario's COVID-19 Science Advisory Table, said the province could have avoided a record-breaking third wave if officials had implemented a lockdown several weeks earlier.

"We'd have a much shorter lockdown right now," he said. "And the important part is just now not to fall into the same trap once more and make the same mistakes."

Caroline Colijn, the Canada 150 Research Chair in mathematics for evolution, infection and public health and a professor at Simon Fraser University in B.C., said both the timing and severity of another surge in Canada will depend on "when we reopen, how fast we reopen, and how many people are vaccinated at the time we do it."

In late April, federal officials suggested that once Canada hits at least three-quarters of the population getting one vaccine dose, it may be possible to start winding down lockdowns over the summer.

Dr. Theresa Tam, Canada's chief public health officer, also noted once 20 per cent of the country has been fully vaccinated, officials can begin easing the most stringent restrictions and, "if you're careful," there won't be a resurgence.

With that in mind, Canada is far from out of the woods, according to Juni, who said any missteps could bring case counts right back up again.

"Summer in itself may not be enough to protect us against the fourth wave," he said. "Therefore we need to be prudent."

Summer months will mean more gathering outdoors — and a likely drop in cases — but experts warn that lifting restrictions at the first sign of hope could set the stage for another surge. (Ben Nelms/CBC)

From an epidemiological point of view, the most optimistic scenario would be starting to reopen as the summer winds down, Colijn said, which would still likely spur another surge of cases over the fall and winter into 2022. 

Reopening too soon, she said, before hitting key vaccination targets, would be like cutting off a water supply while still dousing flames.

"We're talking waves, as if they just come, as if they're not a choice," she said. "It's not a wave; it's a fire. It's a smouldering forest fire." 

Ashleigh Tuite, an epidemiologist and mathematical modeller with the University of Toronto's Dalla Lana School of Public Health, maintains that future rises in cases are expected, but agrees policy choices and individual actions will play a role in how those play out. 

If another wave does happen in the fall, while provinces are likely lifting restrictions, she's hopeful that vaccinations will make a difference — so that a rise in cases wouldn't spur the kind of rise in serious infections and hospitalizations that provinces are currently experiencing. 

"But that doesn't mean that we won't still see infection circulating," she said. 

WATCH | Don't make same 'mistakes' in order to avoid 4th wave:

Don't make same 'mistakes' in order to avoid 4th wave

1 year ago
Duration 1:00
Dr. Peter Juni, scientific director of Ontario’s COVID-19 Science Advisory Table, says policy makers need to avoid making the same mistakes from earlier in the pandemic to avoid a dire fourth surge in cases.

COVID-19 set to become endemic illness

Colijn stressed there's a chance hospitalizations could rise sharply yet again if a significant portion of the population remains unvaccinated, including any essential workers, which she said speaks to the need to prioritize high-risk groups.

"This may become a seasonal, flu-like thing — but right now the impact of that would mainly land on people who did not accept the vaccine," she said.

Juni considers the fall a transition point, when the short-term crisis of this pandemic starts to shift into COVID-19 becoming endemic, meaning a base level of infection remains within Canada's borders and may show up annually like the flu.

That situation speaks to the need for booster shots to adapt to any variants emerging from largely-unvaccinated regions of the world, he said, with some already in development from major vaccine manufacturers.

"And it will indeed be the case that perhaps from 2022 onwards, we will just get accustomed to the fact that we don't only have flu, and the common cold, but we also have COVID-19 out there," Juni added.

Infectious disease specialist Dr. Srinivas Murthy, an assistant professor of medicine at the University of British Columbia, agreed this illness will linger on as one that's endemic in many areas "for quite some time."

"This winter, regardless of where our vaccine uptake will be, there will be cases in our ICUs that will emerge periodically," he added. "But hopefully not a full-blown surge."

Rising vaccination rates, thanks to clinics like this in Mississauga, Ont., are starting to help to bring daily new cases down in some hard-hit regions. (Evan Mitsui/CBC)

Lessons from U.K., Israel

While a return to full normalcy remains months away, and COVID-19 will likely lurk as a lingering, seasonal threat, there are reasons to be hopeful that Canada's vaccination efforts will usher in a new phase of post-pandemic life.

In the U.K., where more than two-thirds of all adults 18 and up have now had at least one dose and roughly a third are fully-vaccinated — with more than 50 million shots doled out — there's a clear roadmap toward reduced restrictions.

Already, residents are enjoying outdoor dining, and all social restrictions are expected to be lifted by June 21.

Colijn noted in some age groups in the U.K., there has been upwards of 90 per cent uptake for vaccinations. While the U.S. is now reporting state-by-state struggles to fill appointment slots, she's hopeful the situation across the pond is a more natural comparison for Canada.

"Hopefully we can learn from that experience," she said.

WATCH | U.K. begins to lift COVID-19 restrictions:

U.K. begins to lift COVID-19 restrictions

1 year ago
Duration 2:01
For the first time in months, many in England could enjoy a pint on a patio Monday as lockdown restrictions started to ease. The government credits the success of its vaccine program, which has seen 32 million people get at least one dose.

Much like the U.K.'s high vaccination rates and tiered approach to reopening, Tuite noted Israel also offers lessons — and hope — for Canadians. 

The country has one of the highest vaccination rates in the world, with more than 10 million doses administered and roughly six in every 10 residents now fully vaccinated.

"What Israel did was, first of all, they had restrictions in place while they were vaccinating, they got case counts down, and then they slowly reopened," Tuite said. "And I think that's what really needs to happen in order to prevent these resurgences."

Juni, however, stressed that the U.K., Israel, and U.S. are not only ahead in their vaccination programs, but also dealt with staggering infection rates at many points in the pandemic, compared to Canada. Those populations may have even higher levels of immunity, thanks to more people being infected before vaccines rolled out.

That means Canadians, and policy makers in particular, need to be cautious about reopening slowly and carefully, he warned, and should not assume we can follow the timelines of other countries.

"The constellation of having quite a large proportion of people vaccinated, plus [lower] case numbers, plus the measures in place to protect people, will allow us to open again."

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Lauren Pelley

Senior Health & Medical Reporter

Lauren Pelley covers health and medical science for CBC News, including the COVID-19 pandemic, Canadian health policy, and the global spread of infectious diseases. She's based in Toronto. Contact her at:

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