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A health care worker speaks to a test patient, a staff member portraying the role of a patient to ensure the assessment systems are working, as they prepare for the opening of the COVID-19 Assessment Centre at Brewer Park Arena in Ottawa, during a media tour on March 13, 2020.

Justin Tang/The Canadian Press

The COVID-19 pandemic in Canada could continue for months, but what happens in the next few weeks will be crucial in determining the character of the outbreak and the toll it takes.

With the number of cases spiking sharply in the past 48 hours, officials are continuing to stress the need to practice public-health measures such as social distancing in the short term, even while the length of time such measures will be needed remains unclear.

“When you see the rise in the curve, what I’m trying to say is, now, the goal is to see how much we can level it off, and don’t let it take off," Theresa Tam, Canada’s chief public health officer, said on Monday.

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The statement reflects a well-studied relationship that suggests the peak of a pandemic can be reduced and delayed by public health measures that inhibit close contact among people and reduce transmission rates.

What is much harder to forecast – and where many countries are now in uncharted territory – is the degree to which individuals, communities and economies can sustain such measures.

“We’re much better at modelling things that people don’t react to,” said Jonathan Dushoff, a biologist at McMaster University in Hamilton who has been studying the spread of COVID-19.

The uncertainty stems from the fact that a pandemic is more like a marathon than a sprint. In many parts of Canada, people have spent the past few days stocking up on supplies and hunkering down at home, just as they might for a severe winter storm. The pattern is a familiar one when the approaching weather hazard could affect daily life for a week or two.

That is not the scenario expected from COVID-19.

Based on how easily the new coronavirus is transmitted – about five new infections for every two – and the average time it takes for the number of infections to double – about six days – a simple model Dr. Dushoff and Ben Bolker, also at McMaster, posted on Twitter over the weekend suggests the epidemic would take nearly two months to reach its peak with no health measures in place. This agrees with projections that epidemiologists have been working with since the basic characteristics of the virus became known.

It is also a worst-case scenario, because it involves the rate of infections peaking so steeply that the health-care system is overwhelmed with severe cases, even though most are relatively mild.

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Now that public health measures are in place, the situation is more complex. If they are effective, the peak could be significantly reduced and also delayed by another couple of months or more. If they are very effective, there is still a chance – now a vanishingly small one – the virus could be kept from reaching a large fraction of the population. However, if case numbers remain low, that will also present a reason for people to return to familiar behaviour, which would increase transmission rates again and set the stage for COVID-19 to rebound with another and possibly greater surge.

DELAYING THE ONSET

​A simple mathematical model based on the

characteristics of COVID-19 shows how reduced trans-

mission through public-health measures (social

distancing) can moderate and delay the onset of peak

infection. However, this does not take into account the

possibility that social distancing will loosen over time,

which could generate a second peak, or the unknown

effect of the changing seasons on virus transmission.

Proportion of pop. with active infections

0.25

No measures taken

0.20

20% less transmission

0.15

0.10

40% less transmission

0.05

Health measures

0.00

200

0

50

100

150

250

Time (days)

DRIVING DOWN THE PEAK

At top left is the peak number of new infections and the

total number of cases if no public-health measures are in

place. As health measures become more effective

(moving right), both the peak and the total number of

cases are reduced. The height of the peak falls more

quickly with improved measures. When transmission is

cut by 60 per cent the peak nearly disappears.

0%

Reduction in

cases

Reduction in cases

25%

50%

Total

75%

More effective health measures

Peak

100%

0%

20%

40%

60%

Reduction in transmission (strength of social distancing)

JOHN SOPINSKI/THE GLOBE AND MAIL

SOURCE: Ben Bolker and Jonathan Dushoff,

MCMASTER university

DELAYING THE ONSET

​A simple mathematical model based on the characteristics of

COVID-19 shows how reduced transmission through public-

health measures (social distancing) can moderate and delay the

onset of peak infection. However, this does not take into

account the possibility that social distancing will loosen over

time, which could generate a second peak, or the unknown

effect of the changing seasons on virus transmission.

0.25

Proportion of pop. with active infections

No measures taken

0.20

20% less transmission

0.15

0.10

40% less transmission

0.05

Health measures

0.00

200

0

50

100

150

250

Time (days)

DRIVING DOWN THE PEAK

At top left is the peak number of new infections and the total

number of cases if no public-health measures are in place. As health

measures become more effective (moving right), both the peak and

the total number of cases are reduced. The height of the peak falls

more quickly with improved measures. When transmission is cut

by 60 per cent the peak nearly disappears.

0%

Reduction in

cases

Reduction in cases

25%

50%

Total

75%

More effective health measures

Peak

100%

0%

20%

40%

60%

Reduction in transmission (strength of social distancing)

JOHN SOPINSKI/THE GLOBE AND MAIL, SOURCE: Ben Bolker

and Jonathan Dushoff, MCMASTER university

DELAYING THE ONSET

​A simple mathematical model based on the characteristics of COVID-19 shows

how reduced transmission through public-health measures (social distancing)

can moderate and delay the onset of peak infection. However, this does not

take into account the possibility that social distancing will loosen over time,

which could generate a second peak, or the unknown effect of the changing

seasons on virus transmission.

0.25

No measures taken

0.20

Proportion of pop. with active infections

20% less transmission

0.15

0.10

40% less transmission

0.05

Health measures

0.00

200

0

50

100

150

250

Time (days)

DRIVING DOWN THE PEAK

At top left is the peak number of new infections and the total number of cases

if no public-health measures are in place. As health measures become more

effective (moving right), both the peak and the total number of cases are

reduced. The height of the peak falls more quickly with improved measures.

When transmission is cut by 60 per cent the peak nearly disappears.

0%

Reduction in

cases

25%

Reduction in cases

50%

Total

75%

More effective health measures

Peak

100%

0%

20%

40%

60%

Reduction in transmission (strength of social distancing)

JOHN SOPINSKI/THE GLOBE AND MAIL, SOURCE: Ben Bolker and

Jonathan Dushoff, MCMASTER university

Even if the pandemic remains active through the spring, a levelling off of the daily situation could gradually reduce media attention and cause people to lose interest in adhering to public health measures, said Jane Heffernan, director of communication for the Centre for Disease Modelling at York University.

Dr. Heffernan, who has modelled precisely such a situation in the case of a flu outbreak, also noted that if the virus retreats in warmer weather, as flu does, there is reason to be concerned about a return in the fall. That second wave would coincide with cooling temperatures and increasing social contact with students back in school.

And, she added, another variable that is confounding predictions is the unknown degree to which mild or asymptomatic cases of COVID-19 are under-reported. Because they are invisible, only measures applied to the entire population will keep such cases from spreading the virus.

“I do expect that there is infection that we can’t see that’s happening in the community,” Dr. Heffernan said.

This view is reinforced by a study published on Monday in the journal Science, which found that the rapid initial spread of COVID-19 in China can be explained by numerous undocumented cases in the population before travel restrictions were imposed in late January.

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Dr. Dushoff, whose model shows that social distancing can sharply drive down peak infection rates, said that even if it ultimately proves impossible to contain the virus, public health measures are still buying precious time for researchers to develop treatments and vaccines, and for physicians to learn how to best help patients who are infected.

“There are so many reasons to keep fighting,” he said.

Editor’s note: An earlier version of this story incorrectly stated that Jane Heffernan is the director for the Centre for Disease Modelling at York University. In fact, she is the director of communication.

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