A critical question in getting a handle on coronavirus: What role do kids play in spreading it?

Among the many, many unknowns about the new coronavirus: What role do children play in transmission of the virus that causes Covid-19 disease?

It’s a question that public health experts would love an answer to. Knowing whether kids are innocent bystanders, getting infected if someone brings the virus into their households, or are in fact a population that is stealthily driving this epidemic, would give response planners critical ammunition to use in the battle against the virus.

What’s at stake are decisions about policies that can be hugely disruptive to families and workplaces. Should schools be closed to slow spread when the virus enters new terrain, forcing parents to scramble for child care alternatives or stay home? Should long-term care facilities discourage families from bringing young children to visit grandparents or other aging relatives?

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Though the evidence to date suggests this virus doesn’t inflict severe disease on children, there’s reason to think kids may be helping to amplify transmission. It’s a role they play to devastating effect during flu season, becoming ill and passing flu viruses on to their parents, grandparents, teachers, and caregivers.

While the new virus is from a different viral family, its behavior is more like influenza than its coronavirus cousins, SARS and MERS, making experts wonder if it is doing the same.

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“Flu is clearly driven in part by schools. And we don’t understand what goes on with coronaviruses and kids — especially this coronavirus,” said Marc Lipsitch, an infectious diseases epidemiologist at Harvard’s T.H. Chan School of Public Health.

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School closures could become a reality if the U.S. sees sustained transmission of the virus, said Nancy Messonnier, director of CDC’s National Center for Immunization and Respiratory Diseases. She urged parents this week to do some homework on whether their children’s schools are considering closing if and when the virus starts circulating in their communities, and how those dismissals would be handled.

“All of these questions can help you be better prepared for what might happen,” said Messonnier, adding that she had contacted the superintendent of the local school district where her children go to school to ask about closures.

When news broke in early January that a new virus was spreading rapidly in — and later from — China, parents flooded social media platforms looking for guidance about how serious the threat was to children.

Initial predictions, which have been backed up by data from China, were reassuring. These viruses can be brutal on older adults — particularly the elderly. But for some as yet unexplained reason, children appear to be spared the worst of the disease.

“Coronaviruses in general have a striking age-related disease [pattern],” said Ralph Baric, a leading coronavirus expert at the University of North Carolina. “So the older you are, the more likely you’re going to get severe disease.”

The largest study of cases from China to date illustrates that point graphically. Published by the China CDC earlier this month, it describes more than 44,000 confirmed cases. There were few detected infections among children aged 9 and younger — only 416 or about 1% of the total cases. None of them died.

Even cases among children and teens aged 9 to 19 were rare; there were 549 cases in that group, representing 1.2% of the entire study group. There was a single death in that age group. By contrast, 20% of the roughly 1,400 people 80 and older who contracted the disease died.

It’s not clear whether the low detection rates among young children means those infections are indeed rare, or if they are mild enough that they tend to escape detection. Baric noted several case studies from China that showed a low number of children who, although they tested positive, didn’t have obvious disease. However, CT scans revealed changes in their lungs that are characteristic to this infection.

“It’s not that they’re not getting infection. They’re not getting disease. They’re not getting sick,” said Malik Peiris, a coronavirus expert at Hong Kong University.

Peiris and Baric both think children are probably playing a role in spreading the virus.

“If they are infected, there is no reason to believe that they will not transmit,” said Peiris.

“There’s no evidence for any of this, but given the available data, that is quite a plausible scenario that one needs to think about.”

School closures are one of the tools public health officials often reach for — or at least contemplate — when infectious diseases spread. More than 1,300 schools in 240 communities in the United States closed schools for a time in the early days of the 2009 influenza pandemic, caused by the H1N1 virus.

The CDC had initially recommended that schools close for seven days — it later expanded it to 14 days — if infections started cropping up among their students. Within a few weeks though, when it started to become apparent the virus caused mainly mild disease, the CDC dropped the school closure recommendation. Despite that, as the pandemic progressed, school closures continued to occur — to proactively stem the spread of disease, or because so many staff or students were sick that it didn’t make sense to keep the school open.

The evidence is mixed on how well school closures work to change the course of an outbreak, like delaying the onset or decreasing its peak. Either outcome would make it easier for the health system to handle.

“To some degree, the jury is out on this strategy overall,” said Jeff Duchin, a public health official in Seattle and King County and an infectious diseases professor at the University of Washington.

It also isn’t clear on how long school closures should last. By and large, most school closures are relatively short, stretching only a few days.

There are questions, too, about how practical it is to stop kids from gathering simply by shutting down schools. Some studies and polls have suggested that children often gather in other locations — like libraries and shopping malls — when schools are closed, potentially cutting into any impact a closure might have.

“How long can you keep schools closed and not expect children to gather elsewhere?” Duchin said.

In one poll of 523 parents whose children’s schools were closed during 2009 H1N1 outbreak, 90% said they agreed with the decision, many saying they believed closures were an effective way to reduce transmission of the flu.

But the closures can also take a significant toll, particularly among low-income families. In the same poll, nearly 20% said their child missed free or reduced-cost school meals. Another 20% said they had to miss work.

Only a small fraction of parents said the closures were a major problem, but the disruption remains a consideration for health and education officials as they weigh closures in future outbreaks.

“We would really worry about low-income families who have less financial resilience,” said Gillian SteelFisher, a health policy researcher at Harvard who conducted the poll and who studies the public response to health crises.

If the U.S. saw sustained transmission of the coronavirus, experts said it would be critical for schools to communicate clearly about the reason for the closures — and the need for kids to stay at home and not congregate in other places.