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A man and his child are among the few people at a mobile COVID-19 testing clinic in Montreal on June 10, 2020.Ryan Remiorz/The Canadian Press

Primary schools and daycare centres have not been major sources of coronavirus transmission, according to an analysis of the international evidence released as two of Canada’s largest provinces prepare to unveil their back-to-school plans.

A Canadian review of 33 studies across 16 countries found that young children – particularly those under the age of 10 – are less likely than teenagers and adults to spread coronavirus.

With children, “we don’t see these superspreader events that we see in other congregate settings [involving] adults,” said Sarah Neil-Sztramko, a researcher at McMaster University in Hamilton and one of the authors of the review. “Even in cases where a symptomatic child has gone into a setting and has had close contact with a number of children … they don’t seem to transmit it to the other kids. We see that fairly consistently across the reports that we found.”

When cases of COVID-19 were identified in elementary schools and child-care centres, the virus was most often introduced by and spread among adults, she added.

The new review, released Tuesday, was compiled by the National Collaborating Centre for Methods and Tools (NCCMT), one of six academic collaborating centres set up in response to the 2003 SARS outbreak and funded by the Public Health Agency of Canada.

The NCCMT is the latest organization to try to make sense of the role children play in spreading the coronavirus, a crucial question as provincial governments and school boards refine their policies for September.

British Columbia is scheduled to release its back-to-school plan Wednesday. Ontario is expected to follow suit later in the week.

Even as reassuring reports have trickled in from European countries that reopened their schools in the spring, including Denmark, Finland and Germany, some experts have warned that child-to-child and child-to-adult transmission could be underestimated because many youngsters with COVID-19 have no symptoms and are less likely to be tested.

“Kids in outbreak settings may be the [first] case,” said David Fisman, an epidemiologist at the University of Toronto’s Dalla Lana School of Public Health. “By definition, if a case is asymptomatic, you don’t know what the onset date was.”

As well, some school systems abroad might have been spared because there wasn’t much COVID-19 circulating in their communities at the time, or because they took precautions such as regularly testing students and staff, and requiring masks and physical distancing.

How many coronavirus cases are there in Canada, by province, and worldwide? The latest maps and charts

Schools scrambling to plan safe reopening

When it comes to schools and the spread of COVID-19, “most people don’t give clear answers because I don’t think clear answers exist,” said Srinivas Murthy, a pediatric critical care and infectious diseases specialist at BC Children’s Hospital.

Dr. Murthy said even British Columbia’s safe reopening of schools in June is no guarantee that schools will be safe in September, particularly if the province’s case counts continue to tick up, as they have recently.

B.C. had mostly suppressed the virus when it welcomed 200,000 students back for a partial reopening that limited classes to half their usual head count in kindergarten through Grade 5, and 20 per cent of their usual size in Grades 6 through 12.

There were no outbreaks and only two positive cases, in a staff member at one school and in a teacher at another, according to a B.C. Ministry of Health spokesman.

In Quebec, primary schools outside the greater Montreal area opened May 11 and were available to about half of the province’s 610,000 K-6 primary school students. Schools in Montreal remained closed.

At the peak on May 31, about 44 students and 34 staff members tested positive for COVID-19, according to data the Education Ministry describes as partial.

While most were individual cases scattered across the province, outbreaks of 12 and seven cases took place in two schools, forcing one school to shut down for several days and another class to be sent home for more than a week. By June 19, six confirmed cases remained among students and nine among staff members, tracking with the drop of cases in Quebec as summer started.

In compiling its evidence review, the NCCMT looked at 33 studies available as of July 20, of which 28 had been completed and five were still in progress. Eight were reports, 13 were peer-reviewed studies and seven were studies published on preprint servers, meaning they had not yet been peer reviewed.

Two of the studies were from Israel, which has recently seen a surge in new COVID-19 infections blamed, in part, on schools reopening.

One of the studies, published in the journal Eurosurveillance, described a major outbreak at a Jerusalem high school identified 10 days after schools fully reopened on May 18.

The outbreak at the Grade 7-to-12 school for nearly 1,200 students saw 153 students and 25 staff members infected. The school’s classes were overcrowded, with 35 to 38 students per room, the study found. Masking requirements had been temporarily dropped and the air-conditioning ran non-stop because of a heat wave.

“What can be taken from that, certainly, is that schools are not immune from these kinds of outbreaks,” said Dr. Neil-Sztramko, who is also an assistant professor of health research methods, evidence and impact at McMaster. “But some of the other public-health measures that we know work – like physical distancing, like hand hygiene, like mask-wearing – should really be considered in these settings, particularly for older kids.”

With a report from Les Perreaux in Montreal

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