Canada could avoid the worst of a 4th wave but we're not out of the woods yet

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

Canada will likely face a fourth wave of the pandemic as the highly contagious delta variant continues to spread ahead of borders and schools reopening, but there's growing optimism another surge won't bring the country back to a crisis point.

Canadian immunologists, virologists and infectious disease specialists say we could fare betterthan in previous waves, with a lower rate of serious infections, due to the effectiveness of COVID-19 vaccines and the willingness of Canadians to get vaccinated.

But our rollout is plateauing and there are still huge swaths of the population that are unvaccinated either by choice or due to a lack of access or eligibility including millions of Canadian kids who are heading back to school in just over a month.

"We're going to see rises in case counts at some point again," said Matthew Miller, an associate professor of infectious diseases and immunology at McMaster University in Hamilton.

"Probably similar to last year, as we head into the fall and the cold weather arrives. But those bumps are hopefully just that tiny hills, and not mountains like the earlier waves."

How bad will Canada's 4th wave be?

The severity of Canada's fourth wave will largely be determined bylevels of COVID-19 immunity in the population from vaccines or prior infection, which can prevent community transmission from rising and stop severe cases from overwhelming hospitals.

Canada has had more than1.4 million cases of COVID-19 so far, yet only 2.6 per cent of Canadians were found to have antibodies due to prior coronavirus infection in early 2021.

"The question is is there sufficient population immunity? No," said Raywat Deonandan, a global health epidemiologist and associate professor at the University of Ottawa.

"And the reason for that is because we measure population immunity by recovered cases and vaccinations."

More than 80 per cent of eligible Canadians aged 12 and up have received at least one shot, and more than 60 per cent have had two. But that number drops to about 70 per cent with one dose and just over 50 per cent fully vaccinated when you consider the country's entire population.

Although Canada has "nowhere near enough" immunity yet, Deonandan says we can "artificially create" adequate protection by using interventions like masking indoors to help with "building walls" around unvaccinated Canadians as COVID-19 becomes more seasonal.

"We're seeing the arrival of the endemic phase of this disease in places around the world," he said. "Because mostly they don't have enough people vaccinated it comes down to that."

Delta threatens to drive COVID-19 surge

Another key factor in Canada's ability to fend off a severe fourth wave is the spread of the more contagious, potentially more deadly delta variant, which is driving COVID-19 levels back up in countries around the world.

"We know from watching the U.K., for example, that delta is very, very capable of tearing through unvaccinated people very quickly," said Dr. Dominik Mertz, an infectious diseases physician and associate professor of medicine at McMaster University.

"Any percentage of unvaccinated people in the population are leaving themselves at very, very high risk."

The United Kingdom has seen a rise in COVID-19 levels in recent weeks,putting pressure on the health-care system.Israel has reinstated mask mandates in response to new outbreaks. And the U.S. has seen a surge in undervaccinated states driven by delta.

A new study in the New England Journal of Medicine (NEJM) this week found two doses of the Pfizer-BioNTech vaccine were88 per cent effective against the delta variant, while two shots of the AstraZeneca-Oxford vaccine were 67 per cent effective.

But there are conflicting reports from the real world about vaccine effectiveness against delta, including new data from Israel's health ministry that suggeststhe Pfizer shot is only 39 per cent effective against infections but farbetterat preventing severe illness.

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Dr. Anthony Fauci, director of the U.S. National Institute for Allergy and Infectious Diseases, told CBC's Power & Politics Friday that the U.S. still has a "substantial proportion" of the population that is unvaccinated and at highest risk from delta.

"That is absolutely something we need to correct, because when you are dealing with a variant like the delta variant that is so efficient in spreading from person to person, you are going to see a kind of surge in cases," he said.

"And for those who are vulnerable,like the elderly and people with underlying conditions, the chances of their getting hospitalized increases."

Reopening borders, schools leaves unvaccinated at risk

Canada could also be at increased risk of exposure to delta due to the reopening of the border to U.S. travellers next monthand international travellers in September, along with the return of school, which could put unvaccinated Canadians at higher risk of COVID-19 exposure.

"It absolutely will. In addition, the greater travel that we're doing inside the country is going to increase the risk of variants," said Dr. Allison McGeer, a medical microbiologist and infectious diseases specialist at Toronto's Mount Sinai Hospital.

"We should not be surprised if the delta variant starts to increase quite substantially and we should not be surprised if we have to go back to some level of travel and other restrictions."

The single biggest cohort of unvaccinated Canadians are children under 12, who are not yet eligible for COVID-19 vaccines despite ongoing clinical trials. Experts say the reopening of schools in September could put them at higher risk.

"It's important that we start reporting our percentage vaccinated, including kids, because that's our actual number," said Alyson Kelvin, an assistant professor at Dalhousie University and virologist at the Canadian Center for Vaccinology and the Vaccine and Infectious Disease Organization.

"Considering we want to have herd immunity be above 85 per cent, we're not going to get there without kids."

Until children under 12 are eligible for vaccination in Canada, Kelvin says those who have less effective immune responses from COVID-19 vaccines including older Canadians and the immunocompromised will continue to be vulnerable.

"Children can't be vaccinated and variants such as delta are more highly transmissibleand there seems to be case reports of increased disease severity in kids when they do get infected," she said. "That's something that we need to be watching going forward."

Future variants pose unknown threat

One unknown threat Canada faces is the possibility of more transmissible variants emerging in the weeks and months ahead that could be worse thandelta, as COVID-19 continues to ravage undervaccinated countries around the world.

Canada was hit hard by the alpha variant at a time when our vaccination campaign had not yet picked up steam, and new and more dangerous variants have repeatedly appeared in countries that continue to be hit hardwith each passing wave.

"Definitely we'll see other variants. If they will be more severe or a variant of concernis another question," said Kelvin."But it is an interesting trend that there seems to be an increase in transmissibility with each as time goes on and we see new variants."

That's not typically something that is seen with other circulating viruses like influenza, said Kelvin, meaning the unpredictability of this virus leaves its future an open question.

Miller says COVID-19 will likely become endemic in Canada and around the world, returning each year like the flu, and our ability to control it is contingent on our ability to get more people vaccinated.

"It's going to keep evolving for decades, presumably. It's not going anywhere. But we have astoundingly successful vaccines," he said. "The truth is, there is light at the end of the tunnel. This will end as all things end.

"But if you're not vaccinated, you're definitely at some point going to get infected."

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