The room for maneuver factor: As the coronavirus locks lift, how far can we get back to normal without triggering a second wave?

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On the evening of May 21, 2020, Montrealers relax at Jeanne-Mance Park.

Kate Hutchinson / The Globe and Mail

How many more contacts will be too? As the provinces of Canada lift physical distance measurements, each has a threshold. This is the point where the increase in the average contact rate among individuals in the population is sufficient to trigger a resurgence of COVID-19 cases and a potential return to more stringent distancing measures.

As opportunities for interaction increase, new analysis for The Globe and Mail provides insight into what Canadians can expect in an uncertain situation – and the challenges facing policy makers.

In Ontario, a 20% rate of additional contact between individuals would likely result in a modest increase in the number of cases. This means that health agencies will treat new cases at a regular rate, but at rates similar to those currently experienced in the province. But that changes with 40% or more. Under these circumstances, the number of cases in Ontario is expected to increase rapidly beyond what has been observed so far.

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In British Columbia, neither a 20% increase nor a 40% increase is a problem. At the other end of the spectrum, the latest data suggests that Quebec as a whole may not yet be below the threshold that would allow the measure to be relaxed without increasing the number of driving cases. A more local breakdown would show differences between Montreal and other parts of the province after isolation.

Determining which freedom to grant is an issue that troubles politicians and public health officials across the country. In Ontario, for example, Premier Doug Ford has repeatedly stated that he would not hesitate to re-impose restrictions if the number of cases continues to increase in the province, but did not say when. would consider tightening the rules.

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“I think about it 24/7,” he said on Friday. “And we are seeing peaks and valleys, but I hope we are going to see the trend go down because I know that in the past few days it has increased. And it’s worrying. These are things you think about all night. It’s hard. “

Indeed, a key finding from the Globe analysis is that small changes in contact rates can lead to big differences in the new cases expected. And even if everyone across the country were to adopt identical precautions, the fallout from the reopening will vary by region – dramatically, in some scenarios.

Screening of COVID-19 cases in Ontario by modification of social restrictions

The probability of

falling in the beach

No change in contact rate

Projection

based on

reported cases

20% increase in contact rate

40% increase in contact rate

60% increase in contact rate

MURAT YÜKSELIR / THE GLOBE AND THE MAIL, SOURCE: CAROLINE COLIJN, SIMON FRASER UNIVERSITY; SEAN ANDERSON, FISHERIES AND OCEANS CANADA

Screening of COVID-19 cases in Ontario by modification of social restrictions

The probability of

falling in the beach

No change in contact rate

Projection

based on

reported cases

20% increase in contact rate

40% increase in contact rate

60% increase in contact rate

MURAT YÜKSELIR / THE GLOBE AND THE MAIL, SOURCE: CAROLINE COLIJN, SIMON FRASER UNIVERSITY; SEAN ANDERSON, FISHERIES AND OCEANS CANADA

Screening of COVID-19 cases in Ontario by modification of social restrictions

The probability of

falling in the beach

20% increase in contact rate

No change in contact rate

Projection

based on

reported cases

40% increase in contact rate

60% increase in contact rate

MURAT YÜKSELIR / THE GLOBE AND THE MAIL, SOURCE: CAROLINE COLIJN, SIMON FRASER UNIVERSITY; SEAN ANDERSON, FISHERIES AND OCEANS CANADA

“Different populations are experiencing different epidemics of COVID-19, so the impacts of their reopening are probably not the same,” said Caroline Colijn, who holds the Canada 150 research chair in mathematics for evolution, infection and public health at Simon Fraser University. in British Columbia.

This heterogeneity means that provinces have different leeway as they progress, said Dr. Colijn, who worked with the Globe and Mail in March to generate trajectories for the pandemic under different levels of physical distancing. The exercise revealed the need for strong measures to slow the rate of new infections and avoid overwhelming hospitals with patients in need of intensive care. It also showed that if the measures were lifted too soon and too suddenly, the pandemic would come back in force.

Now, Dr. Colijn has collaborated with other colleagues, including Sean Anderson, a Fisheries and Oceans Canada environmentalist, to examine a different question: when would a relaxation of restrictions on public contact trigger a return to increase in number of cases?

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Since it is not possible to know or measure each factor in a particular region, the results should be taken as a guide for the significant differences between the four provinces which account for most cases in Canada – Ontario, Alberta, BC and Quebec – as well as a selection of American states for comparison. But although they show the impact that increased contact can have, they cannot predict how much contact will actually take place when people start working and socializing under less restrictive conditions.

Unlike Dr. Colijn’s first projection, the mathematics behind these models can now be compared to two months of actual experience on how the pandemic unfolded in different parts of the country. This data, along with what is known about the characteristics of the virus and various estimates of the increase in contact rates, is what goes into each forecast. The contact rates themselves take into account the number of occasions the disease may have spread between individuals in a given case. They are not correlated to the individual actions of a provincial government; how the projections match provincial actions will only become clear after the fact.

COVID-19 cases screened in selected states based on a 20% increase in contact rate

The probability of

falling in the beach

Projection

based on

reported cases

MURAT YÜKSELIR / THE GLOBE AND THE MAIL, SOURCE: CAROLINE COLIJN, SIMON FRASER UNIVERSITY; SEAN ANDERSON, FISHERIES AND OCEANS CANADA

COVID-19 cases screened in selected states based on a 20% increase in contact rate

The probability of

falling in the beach

Projection

based on

reported cases

MURAT YÜKSELIR / THE GLOBE AND THE MAIL, SOURCE: CAROLINE COLIJN, SIMON FRASER UNIVERSITY; SEAN ANDERSON, FISHERIES AND OCEANS CANADA

COVID-19 cases screened in certain provinces

based on a 20% increase in the contact rate

The probability of

falling in the beach

Projection

based on

reported cases

MURAT YÜKSELIR / THE GLOBE AND THE MAIL, SOURCE: CAROLINE COLIJN, SIMON FRASER UNIVERSITY; SEAN ANDERSON, FISHERIES AND OCEANS CANADA

As the provinces reopen, the way in which measures are lifted becomes more diverse, as well as the extent to which provincial guidelines are understood and followed. All of these factors combined produce some increase in the average contact rate between individuals in different locations. This average rate can be estimated and then used to advance the model and see what happens next.

Existing data and Dr. Colijn’s projections appear to be in line with other studies, including one published online Tuesday by a Canadian-American team examining how public awareness of the pandemic is affecting infection rates. Instead of the infection curves going up and down symmetrically, such models project a steep climb, followed by a long shoulder or an outgoing tray.

“The message is not too confident. Don’t assume that because you’ve reached the top, you have a lot of momentum to come back down, “said Jonathan Dushoff, biologist at McMaster University in Hamilton, who studied the pandemic and was co-author of the study. .

This is also the message of public health officials. Dr. Horacio Arruda, director of public health for Quebec, warned residents on Friday not to lower their guard as the province detailed its plans to lift restrictions on museums, libraries and cinemas. Warmer weather, he said, could make people ignore the rules.

“You know, being away from others is not natural for humans – especially when the weather is nice, we are outside, we go back to our own reflexes,” said Dr Arruda.

Dr Arruda said that was the reason for the province’s gradual approach to reopening, allowing limited outdoor gatherings of up to 10 people from three households starting on Friday. If the rules are not followed, the number of COVID-19 cases could increase rapidly, forcing the province to close the shutters, he warned.

“And everything we did to get there could [turn around] very quickly, “said Dr. Arruda.

The models can also be applied to American states which could be likely sources of interaction once the international border is reopened. Although the number of cases and death rates vary, models suggest that Ontario and Quebec are more like the counterparts of New York and Michigan than British Columbia. is close to Washington State or California. This means that British Columbia would be more likely to see its case numbers increase with the resumption of cross-border traffic.

Screening of COVID-19 cases in certain provinces, based on a 20% increase in the contact rate

The probability of

falling in the beach

Projection

based on

reported cases

MURAT YÜKSELIR / THE GLOBE AND THE MAIL, SOURCE: CAROLINE COLIJN, SIMON FRASER UNIVERSITY; SEAN ANDERSON, FISHERIES AND OCEANS CANADA

Screening of COVID-19 cases in certain provinces, based on a 20% increase in the contact rate

The probability of

falling in the beach

Projection

based on

reported cases

MURAT YÜKSELIR / THE GLOBE AND THE MAIL, SOURCE: CAROLINE COLIJN, SIMON FRASER UNIVERSITY; SEAN ANDERSON, FISHERIES AND OCEANS CANADA

COVID-19 cases screened in certain states

based on a 20% increase in the contact rate

The probability of

falling in the beach

Projection

based on

reported cases

MURAT YÜKSELIR / THE GLOBE AND THE MAIL, SOURCE: CAROLINE COLIJN, SIMON FRASER UNIVERSITY; SEAN ANDERSON, FISHERIES AND OCEANS CANADA

“It puts low-risk places at a higher risk and that’s something to worry about,” said Dr. Colijn.

Another Ontario-specific modeling study was published this week in the journal Biology. Jianhong Wu, mathematician and infectious disease specialist at York University in Toronto, led the study. Its results showed that efforts to reduce the spread through reduced contact rates must go hand in hand with other public health strategies, including wearing a mask, increasing testing, contact tracing and isolation. new cases, to be effective.

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Without such a concerted and organized effort, the likely outcome is a return to distancing, with even less public enthusiasm.

“I don’t think the public can tolerate a second lockout. This is why we have to be very careful, “said Dr Wu.

All models point to the fact that, although the virus is transmitted between individuals, it is the sum of the actions taken by each – combined with effective public health strategies – that will determine whether the breathing room purchased by stopping two months can be made to last.

In essence, COVID-19 has made freedom a shared resource – and a limited resource – which should be used with care.

For Françioise Baylis, a philosopher specializing in bioethics at Dalhousie University, this emphasizes where it should be: on public health rather than trying to design individual escape hatches such as immunity passports which , in theory, would allow some people to return to life as normal while others remain in complete isolation. In comments published this week in the journal Nature, Dr. Baylis and a co-author based at Harvard University set out a multitude of reasons, both ethical and practical, why such a system is unworkable.

“The real problem here is that we are all in the same boat and if we all want to get out of it, we have to take care of each other,” said Dr. Baylis.

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