Need an expert? COVID-19: the Canadian projections

Posted on Friday, April 17, 2020

Coronavirus planet

Members of the media may directly contact the following expert:

Dr. Ann Jolly (English only)
Associate Professor, School of Epidemiology and Public Health, Faculty of Medicine


Dr. Ann Jolly has been closely watching the pandemic and the Canadian coronavirus projections.

She researches the spread of pathogens through social networks of connected people and has taught a course in infectious disease epidemiology since 2000, using real data to create surveillance systems and detect outbreaks.

Dr. Jolly agreed to answer our questions:

1- Canada seems to be making progress at flattening the curve. Should physical distancing measures continue? Why and for how long?

“We have to be very careful in determining when the peak of the outbreak is reached. It may be too early to tell, for several reasons.

  • When looking at a graph or number of recent cases, they will always seem to be declining, because cases take a certain amount of time to diagnose, and then to report. 

    For example, we have had issues in accessing test kits in Canada and only some people meeting certain criteria were being tested, and then only some of these people would have to be tested to rule out other things before being tested for SARS-CoV-2. Then the positive report has to get to public health staff to be counted in with Ontario’s total. That can take a number of weeks, up to 6 weeks sometimes. So, unless you know the delay time and can correct for it, the numbers will be incomplete. This is actually what happened in SARS where the outbreak was declared over before the diagnostic and reporting delays were factored into the daily cases.
  • The second thing is that we need to know far more about the natural history of the infection before we can start relaxing the isolation. We still don’t know how many asymptomatic people are infected, whether they shed virus, or whether those who have had it are immune, and how many people in the general public may be immune.
  • And finally, we need to know how the virus is evolving. Does it replicate very fast and inaccurately and recombine with other viruses such as the ‘flu?”

2- Is Canada still at risk of a surge? What can we expect from the next ‘’waves’’?

“Canada will still have surges as the virus gets into pockets of connected people where it was not previously able to go. This is clearly shown in the technical briefing for the Canadian projections, and is consistent with what was observed in SARS, with other propagated person to person outbreaks, and transmission of infection through social networks of connected people. 

The waves will usually be in people who may not have been previously exposed, so it is difficult to say exactly who will be affected.”

3- When should schools reopen? Should it be before the end of this school year, or next September?

“This is an important question. The first thing to keep in mind is that not all people should return to work at one time because this is likely to result in a large surge. When dealing with infection in a network, a synchronized approach is essential.

A better option would be to test a representative sample of people to see how many are infected, and/or immune and if that proportion seems manageable to gradually let portions of residents return to school and work. Having said this, poverty is a big killer, and we do need to ensure that during this time and afterwards people have adequate incomes.”

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