As children make up fewer than 2% of reported Covid-19 cases globally, health officials around the world are considering when to reopen schools—but researchers warn that studies on whether children can transmit the new coronavirus have shown mixed results.

Officials consider reopening schools as Covid-19's spread slows

Officials around the world are trying to determine which parts of society to reopen as the rates of newly reported cases of Covid-19, the disease caused by the new coronavirus, decrease. Worried that staying home from school could hinder children's education and prevent adults from returning to work, countries such as Denmark, Germany, and others are sending children back to school, with other countries, such as France, planning to reopen schools in coming weeks.

Switzerland also is considering loosening social distancing restrictions for children, under the assumption that children with Covid-19 pose very little risk of transmitting the virus to adults, Vox reports. Daniel Koch, the country's infectious disease chief, said one study released this month shows that young children under 10 years old rarely get or transmit the new coronavirus.

"When they get sick, they often have only light symptoms," Yann Hulmann, a spokesperson for the Swiss Federal Office of Public Health, told Vox. "They are apparently not big spreaders and are often infected by adults. So reopening schools does not seem to be a major problem."

Research offers mixed results

So far, researchers agree that children are not contracting the new coronavirus at the same rate as adults. According to CDC, children under the age of 18 account for under 2% of reported cases of Covid-19 in China, Italy, and the United States.

But research has yet to show whether young children transmit the new coronavirus at a similar rate as adults. "What we don't know yet is the degree to which children can transmit the virus," said Danielle Zerr, an infectious disease expert at Seattle Children's Hospital.

For example, one pre-published study by researchers at the University of Queensland in Australia that observed a collection of families with Covid-19 across the world found that children were the initial source of infection among the families in about 8% of households, Nature reports.

Another study by researchers at New South Wales' National Centre for Immunisation Research and Surveillance published last month that looked at staff and students at five primary schools and 10 high schools from March to mid-April found that, out of 863 people who were in close contact with someone with Covid-19, only two, or 0.23%, contracted the new coronavirus. The researchers concluded that transmission of the coronavirus "in children in schools appears considerably less than seen for other respiratory viruses, such as influenza."

And a third study that examined a cluster of Covid-19 cases in the French Alps found that a nine-year-old who attended three different schools while showing symptoms of Covid-19 didn't infect anyone. "It would be almost unheard of for an adult to be exposed to that many people and not infect anyone else," said Alasdair Munro, a pediatric infectious-diseases researcher at University Hospital Southampton.

John Edmunds, a member of Britain's Scientific Advisory Group for Emergencies, noted that, so far, there's "only one documented [Covid-19] outbreak associated with a school." He said, "[Y]ou would normally expect most of the outbreaks to be associated with schools but yet in global literature there is only one documented study. … It is pretty remarkable."

But not all health experts—or research—are in agreement.

For instance, in one study released by Christian Drosten, Germany's chief virologist, researchers wrote that they "found no significant difference" in the viral loads of the new coronavirus "between any pair of age categories, including children." Based on their findings, the researchers concluded that "[c]hildren may be as infectious as adults," and recommended that countries practice "caution against an unlimited re-opening of schools and kindergartens in the present situation."

Kristine Macartney, lead author of the study on children in South Wales schools, noted that the preliminary study did not account for whether schools had implemented social distancing measures, and she suggested the results shouldn't be used as a basis for reopening schools.

"We did see low transmission," but "we didn't see no transmission," Macartney said. "I think children can still transmit coronavirus. That's certainly the case. We've seen that."

Further, Gary Wong, a researcher in pediatric respiratory medicine at the Chinese University of Hong Kong, said widespread school closures and a comparatively lower rate of testing for the new coronavirus among children could contribute to the low number of reported cases of Covid-19 among the group.

Wong added that, since plenty of other respiratory viruses can transmit between adults and children, it would be odd if the new coronavirus didn't have some level of transmission between the groups, as well.

"I don't believe this virus is an exception," Wong said. "As long as there is community transmission in the adult population, reopening of schools will likely facilitate transmission, as respiratory viruses are known to circulate in schools and day cares."

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What the findings mean for moving forward

In light of the conflicting evidence, some health officials are waiting for more research results before reopening schools and easing social distancing restrictions for children.

CDC warns that all people with Covid-19, including those with mild cases of the disease and children, "can still pass this virus onto others who may be at higher risk, including older adults and people who have serious underlying medical conditions."

And while the European Center for Disease Control and Prevention (ECDC) has said data indicates that "children are unlikely to be primary source cases" for Covid-19, Alexandru Niculae, a spokesperson for the agency, told Vox that the data currently available "cannot be considered as 'enough evidence'" to definitively state that children cannot transmit the disease.

According to Nature, countries that are reopening schools will serve as test cases. If children are contributing to the new coronavirus' spread, Covid-19 cases likely will spike in those countries as they return to school.

But some health experts argue that shouldn't be the case.

"Are any of these studies definitive? The answer is 'No, of course not,'" said Jeffrey Shaman, an epidemiologist at Columbia University who was not involved in the studies. As such, "to open schools because of some uninvestigated notion that children aren't really involved in this, that would be a very foolish thing," Shaman said (Ward, Vox, 5/2; Beasley, Reuters, 5/19;  Malapaty, Nature, 5/7; Faulconbridge, Reuters, 5/19; Jankowicz, Business Insider, 5/22; Mandavilli, New York Times, 5/8).