Calgary

COVID's R-value (or ability to spread) is once again rising in Alberta

The average number of COVID-19 infections transmitted by each diagnosed case is once again rising in Alberta.

Experts say it's important R-value remains below 1, but in some regions it's creeping closer

Albertans enter a COVID-19 mass immunization clinic in downtown Calgary in May 2021. COVID-19's R-value, or its ability to spread, has been increasing in the province in recent weeks. (Jeff McIntosh/The Canadian Press)

The average number of COVID-19 infections transmitted by each diagnosed case is once again rising in Alberta.

Over the last two weeks, Alberta's provincewide R-value was 0.84, with a confidence interval of 0.74 to 0.94. It was even higher in Edmonton, at 0.97 with a confidence interval pushing the city's R-value potentially over one. 

The R-value represents the number of people infected by each infected person. 

Those numbers are up from previous weeks, when the R-value was 0.75.

The issue is whether or not we are going to see in Alberta what's happening in the United States and what's happened in the U.K.- Dr. Chris Mody

Dr. Chris Mody, the head of microbiology, immunology and infectious diseases at the University of Calgary, says while it's good that cases are down, the R-value (or reproduction value) shows the rate at which cases are dropping is plateauing.

"Right now, we're doing great," he said, adding that the province likely won't see the impacts of decreased public health restrictions until early August. 

"What becomes an issue is if that R-value creeps up to one and then starts to increase — and we don't know the answer to that in terms of how the decrease in restrictions will affect that R-value."

Mody said it's important the R-value remains below one.

At an R-value of one, each person with COVID-19 transmits it to just one other person. If that number is above one, case numbers grow. But once it falls below one, it means cases are decreasing. 

For COVID-19, research suggests the R-value averages around 2.6 to 2.7 with no interventions in place — like masks or physical distancing — meaning if left unchecked it could spread exponentially.

So the R-value depends on not just how infectious the coronavirus is, but how effective society is at stopping it from spreading. 

"We know that no matter what we do in terms of changing things, that cases lag a couple of weeks behind that. And so if you think about the day the [Calgary] Stampede finishes, you know, then the effect of that will be two weeks later," Mody said. 

Vaccinations will be key to stopping that spread, he added.

"The issue is whether or not we are going to see in Alberta what's happening in the United States and what's happened in the U.K. And that's based on delta variant causing infections predominantly, although not exclusively … in people that are unvaccinated. And that therein lies the risk."

The delta variant is more transmissible and has caused surging new cases in regions like the U.K. There have been 906 delta variant cases in Alberta; 351 of the province's 599 total active cases are variants. 

Nearly half of Alberta's population has been fully vaccinated against COVID-19.

Trevor Tombe, an economics professor at the University of Calgary, said where the province lags behind is in the share of the population having received a first shot. 

"Other provinces have a much larger share of their populations that have received that first shot. So, it might be the case that Alberta and Saskatchewan have a much tougher challenge in terms of vaccine hesitancy and that's really going to potentially bite over the next couple of weeks," he said. 

Tombe's projections show Ontario will have 80 per cent of its population vaccinated with at least one shot by the end of July, while Alberta will be lower at 75 per cent.

With files from Jennifer Lee

Comments

To encourage thoughtful and respectful conversations, first and last names will appear with each submission to CBC/Radio-Canada's online communities (except in children and youth-oriented communities). Pseudonyms will no longer be permitted.

By submitting a comment, you accept that CBC has the right to reproduce and publish that comment in whole or in part, in any manner CBC chooses. Please note that CBC does not endorse the opinions expressed in comments. Comments on this story are moderated according to our Submission Guidelines. Comments are welcome while open. We reserve the right to close comments at any time.

Become a CBC Member

Join the conversationCreate account

Already have an account?

now