Highly contagious delta variant could be Alberta's primary strain by late June, scientists warn
Many are at risk until most of the population is fully vaccinated, doctors say
When the alpha variant of coronavirus first began to spread in Alberta early this year, Gosia Gasperowicz sounded the alarm that the province was headed for a third wave which would likely be worse than the previous two.
Now, she and other experts are warning the delta variant could take over as Alberta's dominant strain by the end of June — potentially bringing a fourth wave of COVID-19 cases in the fall, unless action is taken.
"Beginning of March it was super clear, and still it was downplayed … but it was really clear that we [were] heading to the third wave and similarly now it is very clear that we are going to the fourth wave," the developmental biologist with the University of Calgary said.
A total of 344 cases of the delta variant have been identified in Alberta, an increase of 82 cases since Friday. Nearly all of those cases are in Calgary.
Variants account for about 76 per cent of Alberta's 3,000 active cases, which are down by 20,000 in the last month. Most of those cases are the alpha variant.
Gasperowicz said delta variant cases are doubling roughly every six to 12 days. With a doubling time of eight days, she said delta will become the dominant strain around June 26. If it doubles at a more conservative prediction of every 12 days, the variant would become the dominant strain around July 5.
"We are in exponential [growth] now," she said. "It's the same story."
In a worst case scenario that could mean daily case counts once again in the thousands — a projection that doesn't factor in the future negative effects of loosened restrictions, or the positive effects of higher vaccination rates, Gasperowicz said.
Delta grows exponentially in AB<br>It seems to be doubling every 6–8 days<br><br>At such rate we can expect:<br>500 daily new cases on Jul 18<br>2000 daily new cases on Aug 03<br><br>To stop such growth we'd need at least 70% population FULLY vaccinated AND public health orders from Stg1 or earlier. <a href="https://t.co/dPDoc7OFOS">pic.twitter.com/dPDoc7OFOS</a>—@GosiaGasperoPhD
Dr. James Talbot, co-chair of the Edmonton zone medical staff association's strategic COVID committee and a former chief medical officer of health for Alberta, said he has increasingly been feeling a sense of deja vu.
He thinks reopening before the province hits 70 per cent of people fully immunized — not just with one dose, the current benchmark — is a mistake.
"What we're looking at is the potential for a fourth wave to complicate what happens in September with trying to get kids into school and people back to work," he said.
Studies out of the United Kingdom, where the delta variant has driven a surge of new cases, show only about a third of people are protected against symptomatic cases of the variant after a single shot.
Both AstraZeneca and mRNA vaccines are estimated to be 92 to 96 per cent effective against hospitalization after two doses.
2 doses needed
Talbot said it's important to remember that right now no children under 12 are vaccinated and the majority of those vaccinated only have one dose, so are largely unprotected from the delta variant.
"Pushing for the 70 percent of [one dose] is giving people a false sense that that's the end, that after that everything is fine," he said.
"If you get in the 70 to 80 per cent range with people who are protected [with two doses], you can protect even those who haven't gotten the vaccine. That's literally what herd immunity means."
He said the greater the number of infected people, the greater the risk of the virus mutating into more infectious or deadly variants.
Talbot said he'd like to see the province move more cautiously, and be more transparent in sharing its internal modelling on variant transmission.
Chief Medical Officer of Health Dr. Deena Hinshaw acknowledged concerns over variants during a press conference last week, as she announced expanded eligibility for second doses of vaccine.
"As we continue to face COVID-19 and its emerging variants, the sooner we can get everyone fully immunized, the better," Hinshaw said.
"I have stressed for months that one dose of the vaccine provides good protection — and it does. The evidence that we are seeing in Alberta, however, shows a significant jump in effectiveness after receiving the second dose."
Dr. Alain Tremblay, a professor of medicine at the University of Calgary and respirologist at Foothills hospital, said it's worth noting that exponential growth curves look flat at first.
"That's what they saw in the U.K. … even the U.K. variant is not the U.K. variant anymore," he said. "[Delta] clearly has more staying power than the alpha [variant] ... the question is, is it going to replace it and we stay at 100 cases per day, or is it going to replace it and we're gonna have another wave."
Tremblay said he was fairly comfortable with earlier stages of reopening, but as Alberta prepares to lift all restrictions, he's worried.
"I'm really concerned what we're going to do July 1," he said. "Are we going to be extremely aggressive with contact tracing? … Or are we just going to say oh, it's phase three, we're not doing anything. And really there's been no clarity on that, not that I've seen."
Dr. André Corriveau, Alberta's deputy chief medical officer of health, said Tuesday that as overall cases decrease, more transmissible variants will become predominant by default.
"We're watching and certainly trying to do all we can still with the public health measures in place to contain it in the Calgary area … we are still confident that our strategy is aimed in the right way to get as many Albertans immunized as possible as soon as possible," he said.
Corriveau said modelling to predict case growth of the delta variant in Alberta is underway, but it hasn't been completed yet. He added that he does not have precise details about what measures will remain in place to combat transmission as the province reopens.
Gasperowicz said the fourth wave may already be growing — it's just that the delta case growth isn't obvious due to overall case decline.
"It's already here, it's just invisible."
With files from Jennifer Lee