Federal COVID-19 epidemic modeling scenarios released Thursday show a rosier picture than projections Saskatchewan released a day prior, though the country’s chief medical health officer warned the nation cannot get complacent.
The federal government said that prior to more stringent public health controls, each infected person in Canada was spreading the virus to an average of 2.19 others. The goal of public health measures, such as social distancing, contact tracing and case quarantines, is to reduce the number of others infected by each case to less than one. Then, the government said, the virus will die off.
That number, 2.19, is lower than any of the three scenarios presented in Saskatchewan’s modeling Wednesday. The province assumed a per-case spread of 2.4, 2.7 and four people, based on its own estimates for the spread in Wuhan, China, low-Italy and early Canadian spread respectively.
On Thursday, Tam acknowledged that individual jurisdictions, such as provinces and territories, may have different models, and the numbers presented by the federal government represent a whole-of-country look.
She said what Canada has is a group of regional epidemics, with the majority of cases so far seen in B.C., Ontario, Alberta and Quebec and some regions, such as Nunavut, yet to report a single case.
The numbers she presented included three ranges: no control, some control and high control.
In the short term, Canada could see between 22,580 and 31,850 cases by April 16, and a total of between 500 and 700 deaths.
Longer-term, the picture is less clear. But dynamic modeling, which examines a number of possible outcomes using existing projections and data of the virus’ behavior, shows that more successful pandemic controls could lead to between 11,000 and 22,000 deaths, while weaker controls would lead to a direr outcome of between 100,000 and 250,000 deaths.
The difference between those scenarios is the ability of the country to control the epidemic’s spread through a combination of social distancing and successful contact tracing and isolation.
Under the strong epidemic control scenario, between one and ten per cent of the Canadian population would be infected. The curve in that scenario would peak in the late spring to early summer and the epidemic curve would end by the fall.
Under the low control scenario, though, the peak wouldn’t hit until late summer and the curve itself wouldn’t end until spring 2021.
Under that low control scenario, millions more would become infected and thousands more would die.
The government stressed that neither of the modeling scenarios are predictions. Rather, they’re possibilities used to guide health system planning.
“Models are not a crystal ball and cannot predict what will happen,” Tam said.
Rather, they’re useful to plan for the worst but aim for the best.
“These stark numbers tell us that we must do everything we can now to remain in that best-case scenario to stay in the lower range of the green zone with strong epidemic control,” Tam said.
“Our collective efforts despite all the hardships and the cost is critical as we must minimize the population infected in order to keep deaths, ICU admissions and hospital admissions as low as possible. The resolve and level of effort of all Canadians … will ultimately determine whether we can remain in this best-case scenario and ensure that our health system can cope. We cannot prevent every death but must prevent every death that we can.”
Tam said it’s too early to know where Canada falls on the curve, but it is possible to keep the nation in the high-control scenario.
She also said that the country won’t know when it hits the peak until it’s already passed it because it can take up to two weeks for someone to become infected, show symptoms, get tested and receive results.
Even when the peak is reached, public health measures will have to remain in place, she said, until Canada comes all the way down the back half of the curve.
Half of the cases, she pointed out, come on the way down.
“Once we’re past the peak of this first wave, it will be equally critical to maintain our control measures. If we let up … the epidemic will re-ignite. We must stay the course until we reach a very low level of cases,” she said.
And once Canada is through the first wave, and some measures may be lifted, others will have to remain in place so that second waves can’t come from importation and community spread.
That means testing and contact tracing will have to keep going for a significant length of time.
Meanwhile, the better Canada does at keeping the number of cases below the health care system’s capacity, the more lives will be saved and the more time there will be for scientists to develop vaccines and treatments to make COVID-19 even less deadly.
“The country still has an opportunity to control the epidemic and save lives,” Tam said.
“We must prevent all deaths we can. We all play a role in what the future may hold.”
The federal modelling scenarios are available here:
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