The ‘reproduction number,’ or the average number of Canadians who are infected by someone with the novel coronavirus, has been falling since the third week of May, data released by epidemiologists shows.

Nationally, the reproduction number is down to .65, which means that on average three Canadians with the virus will pass it on to another two. In the early stages of the epidemic, in mid-March, one infected person, on average, infected another three.

Infections are falling because of increased use of masks and a lack of gatherings, and warmer weather plays a major role, according to experts Global News talked to. But they say they are uneasy about the fall.

The R number is important because if it strays over one, cases are growing exponentially. One way of expressing this is the number of days it takes for cases to double. As you can see in the following graphs, that period has been steadily lengthening, even in the worst-hit provinces:

Ontario, one of Canada’s worst-affected provinces, has seen a steadily falling R number, now at .54.

“I think it’s falling because we have things under control,” says University of Toronto epidemiologist Ashleigh Tuite. “The question is: why are things under control?”

“The biggest one is that we are seeing is the use of masks indoors as businesses are starting to reopen.”

Warmer weather, during which people spend less time close to each other indoors, is a major factor as well.

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“I think our weather has been our friend in this,” says the University of Toronto’s Colin Furness. “I actually credit the weather with a lot.”

Outdoor gatherings, like large demonstrations in the U.S. and well-publicized incidents like the crowding of Trinity-Bellwoods Park in Toronto, haven’t had a visible effect on infection rates, implying that the virus isn’t transmitted well outside.

“In Toronto, we have the example of the Trinity-Bellwoods situation where there was a lot of mixing outdoors and a lot of concern about that particular event,” Tuite says. “We didn’t see the anticipated surge in cases, so the evidence really at this point does point to the outdoors as being a lower-risk environment.”

“At this point, it really does seem that the virus thrives indoors and does not transmit so well outdoors.”

The flip side of that, however, comes in the fall.

 

Schools and universities will likely open in some form, and colder weather will draw people back inside. By that time, Furness fears, the virus will seem under control, making people “reckless.”

“We’re going to do well in large numbers in September, and then it’s going to tank, several weeks starting from September,” he says. “It needs to spread quite a bit before you get enough for the acute cases, for you to notice that things are getting worse.”

“I think October is when it’s really going to start to hit the fan, and we’d better be ready for that.”

“It feels to me like it’s almost inescapable. I’m afraid that October and November are going to be very bad-news months.”

Tuite is also uneasy about the fall.

“The fall is concerning, because there are a series of factors that suggest that we are potentially going to have a more difficult time with this,” she says.

“I think one of the challenges, when you think about school reopening, is that kids don’t go to school in a vacuum. They go to school and they come home and they interact with other people. The reality is that they have lives outside of school.”

What R numbers don’t show, Tuite explains, is how many people are affected. That’s key to whether a growth in cases is something the health care system can cope with, or whether it threatens to get out of control.

“If you’re in Ontario, and you have 300 or 400 cases that are making 400 new cases every week, that’s going to be hard to sustain in terms of just thinking about contact tracing,” she says.

“At this point, we have public health units who are only doing COVID. All COVID, all the time. They need to get back to their other public health roles and responsibilities. At this point, if we’re talking about this number of cases that need followup on a daily basis, it’s going to be really, really hard to sustain that.”

On the other hand, she says, a high R number among a small group of people could be more manageable:

“Say we’re in a province where we only had five cases reported a day. Those five cases make five new cases over the next week, and they make five new cases over the next week — that’s’ probably pretty sustainable. Public health can manage those cases and manage the contact tracing that they need to do.”

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