Some of Canada’s COVID-19 scenarios ‘unexplained and doubtful’, new report argues

Editor’s note: This story has been updated to include comment received by the Public Health Agency of Canada.

Modelling by Canadian public health officials of the coronavirus pandemic, released last week, fell short of explaining the assumptions behind some of the projections, according to a new report that described them as “unexplained and doubtful.”

One of the researchers behind the report, Amir Attaran, spoke as an expert witness before the parliamentary health committee on Tuesday and slammed the modelling released by the Public Health Agency of Canada (PHAC) as not being transparent enough.

“It contained errors and it was largely unscientific.”

The modelling released by federal public health officials on Thursday laid out three different potential scenarios for how the COVID-19 pandemic could unfold in Canada: one with strong control measures such as high rates of social distancing and testing, one with weaker response measures, and one with no measures taken.

The scenario with strong control measures suggested roughly 11,000 to 22,000 people would die if between 2.5 and 5 per cent of the population is infected with the virus.

If the infection rate hits 25 per cent under the scenario involving weaker control measures, those deaths could spike to more than 100,000 or 200,000 if 50 per cent of the population is infected.

The models also laid out projections for the total number of cases and hospitalizations in both those scenarios.

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Dr. Theresa Tam, Canada’s chief public health officer, said the estimates are based on the best available data so far, and that data can and does change regularly.

A new report released Tuesday — authored by scientists in San Francisco, Berkeley, London and Attaran in Ottawa — argued that PHAC’s “technical basis for arriving at these findings was not disclosed.”

“While the basis for expectations of 70-80% cumulative infection prevalence in the absence of control measures is consistent with conventional results, the technical considerations leading to PHAC’s predictions of 1-10% and 20-50% cumulative infection prevalence under scenarios of ‘stronger’ and ‘weaker’ intervention are unexplained and doubtful,” the report said.

The report called on the federal health agency to make a number of updates to the “technical documentation underlying PHAC projections,” arguing they would “transparently clarify the basis and strength of evidence for interventions that PHAC proposes to mitigate the burden of COVID-19 in Canada.”

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In response to Attaran’s criticisms of PHAC modelling, a statement provided an agency spokesperson said: “Predictive modelling for COVID-19 requires that we make assumptions based on incomplete data and evolving science.

“These assumptions change as we get new information about the virus and more data about the epidemic in Canada. We are continually improving the models to provide the best available information to Canadians about possible outcomes,” the statement said.

Since late January, the House of Commons standing committee on health has been examining the federal government’s handling of the crisis and has heard so far from over 40 government officials, health experts and other stakeholders.

In addition to hashing out what measures have been taken, discussion has turned to how society and the economy will re-open following the first wave of the virus.

As it released its modelling on Thursday, PHAC officials said they do expect “subsequent smaller waves” of the virus after its possible peak in the summer and warned that public health control measures will have to continue to keep those wavelets contained.

On Tuesday, Attaran argued that the “endgame” has to come about through “careful, scientifically tailored stages” because most Canadians “haven’t fought off the virus and developed immunity to the virus.”

“We are just as immunologically susceptible as before,” he told MPs. “If isolation ends for everyone at the same time, we will immediately return to the same hellish spot that we just dodged.

“In the hands of a well-informed public health chief, staging these disease curvelets does not stop people getting sick with COVID-19. It does, though, make it manageable and reduces the number of people dying of COVID-19, short of the vaccine, which is absolutely out of reach in 2020.”

No plans for handling the smaller COVID-19 waves have yet been presented and “we need one now,” Attaran argued.

He urged MPs to act quickly to legislate data sharing between the provinces and the federal government to ensure PHAC’s models are as robust as possible.

“It is impossible for scientists inside or outside government to do the best job planning these curvelets without excellent disease surveillance, data sharing and epidemiological modelling,” he argued.

As of Tuesday, there are 26,146 confirmed cases of the new coronavirus in the country, according to the Public Health Agency of Canada.

The deaths of 823 have been linked to the virus, according to the latest figures.

-With files from Amanda Connolly