With the news Thursday that two children, including a baby boy, are among Ontario’s 17 newly confirmed COVID-19 cases, parents may be understandably anxious about whether kids are at risk from the pandemic.

Research on COVID-19, the disease caused by the novel coronavirus, offers good news and bad news — and the bad news is mostly bad for adults.

The good news is that nearly all cases of COVID-19 in young people are mild, according to the best available evidence on what is still a very new disease.

Kids appear to be significantly less likely than adults to suffer severe symptoms.

The bad news is that researchers suspect children may be particularly likely to boost the spread COVID-19 in families and communities.

That is why closing schools, as Ontario announced Thursday it would do for all publicly-funded schools for two weeks starting after March Break, is such an important measure in trying to slow the outbreak — although it is probably not sufficient on its own.

“There’s a lot of indirect evidence that kids are extremely important,” says Dr. David Fisman, an epidemiologist at the University of Toronto’s Dalla Lana School of Public Health.

“In terms of social-distancing measures to shut this down, you need to close schools as part of this, because kids are great amplifiers of respiratory disease.”

Fisman co-led outbreak modelling research that suggested widespread, early social-distancing measures, including school closures for kids and working from home for adults, would be necessary to prevent massive strain on the province’s healthcare system if community transmission becomes widespread. Asked to comment on the news of Ontario-wide public school closures, Fisman responded with a string of celebratory emojis.

The best available data on how COVID-19 affects children comes from China, where the outbreak was first detected. The World Health Organization’s mission to the country, which was co-led by Canadian Dr. Bruce Aylward, looked at data from all age groups and found that children were far less likely to suffer severe symptoms.

The WHO mission reported that just 2.4 percent of reported cases in a massive Chinese dataset were children under the age of 18. Among that small group, only 2.5 per cent had severe symptoms, and just 0.2 per cent had critical symptoms. That is much less than the population as a whole: 13.8 per cent had severe symptoms and 6.1 per cent were critical, WHO reported.

Later data from the Chinese city of Shenzhen supported those findings, but with a twist; a pre-print study, one that is not yet peer-reviewed, suggested that kids were actually just as likely to catch the disease. But the researchers also found that they were less likely to suffer severe symptoms — suggesting that the very low number of cases in children reported by the WHO mission could be because some children are so mildly affected that they fly under the diagnostic radar.

“Everyone can get this infection. But there’s a growing narrative demonstrating that kids just don’t get that sick,” said Dr. Isaac Bogoch, an infectious disease specialist at Toronto General Hospital and the University of Toronto.

That’s great, because it means we will probably see very few child deaths from COVID-19, says Bogoch.

“But the trouble is, even if they don’t get that sick, they still shed the virus. And if they’re not showing overt symptoms and they’re shedding the virus, they can infect others, including more vulnerable populations,” such as older people with underlying health conditions, who are at highest risk of severe outcomes.

Bogoch also praised Ontario’s decision to close schools for two weeks after March Break.

“Even though kids don’t get that sick, they can still be drivers of this epidemic. School closures, when coupled with other social distancing initiatives, is a smart move.”

While more research is needed on whether kids are especially efficient transmitters of COVID-19, Canadian research on the seasonal flu, a respiratory illness with similar symptoms, gives that hypothesis weight.

Mark Loeb, a scientist at McMaster University, led clinical trials in Canadian Hutterite colonies that tested the efficacy of providing flu vaccines to children alone, a strategy that turned out to be enormously effective in protecting others in the community.

“By vaccinating the children, the effect of doing that was protecting people who never got vaccinated to the same level as if they had had the vaccine themselves,” Loeb said.

The research supported the theory that children are critical drivers of flu-transmission. Loeb said it “would not surprise” him if the same is true of COVID-19, but we need more evidence.

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Toronto Public Health and Peel Region Public Health declined to provide more details about the two child COVID-19 cases, citing privacy concerns. The Ontario Ministry of Health webpage listed both as being in “self-isolation,” meaning they are well enough to recover at home and are not hospitalized.

The girl in Peel Region is the daughter of another confirmed COVID-19 patient who caught the virus through international travel, Peel Public Health’s associate medical officer of Health, Dr. Lawrence Loh, confirmed.

Loh said the whole family was already in self-isolation at home, so there is no risk to the broader community or her schoolmates, and that the girl is recovering well.