In Sweden, day care centers and most schools have remained open throughout the pandemic.

Sipa USA via AP Images

Science’s COVID-19 reporting is supported by the Pulitzer Center.

There’s nearly universal agreement that widespread, long-lasting school closures harm children. Not only do children fall behind in learning, but isolation harms their mental health and leaves some vulnerable to abuse and neglect. But during this pandemic, does that harm outweigh the risk—to children, school staff, families, and the community at large—of keeping schools open and giving the coronavirus more chances to spread?

The one country that could have definitively answered that question has apparently failed to collect any data. Bucking a global trend, Sweden has kept day care centers and schools through ninth grade open since COVID-19 emerged, without any major adjustments to class size, lunch policies, or recess rules. That made the country a perfect natural experiment about schools’ role in viral spread that many others could have learned from as they reopen schools or ponder when to do so. Yet Swedish officials have not tracked infections among school children—even when large outbreaks led to the closure of individual schools or staff members died of the disease.

“It’s really frustrating that we haven’t been able to answer some relatively basic questions on transmission and the role of different interventions,” says Carina King, an infectious disease epidemiologist at the Karolinska Institute (KI), Sweden’s flagship medical research center. King says she and several colleagues have developed a protocol to study school outbreaks, “but the lack of funding, time, and previous experience of conducting this sort of research in Sweden has hampered our progress.”

“We are trying to mobilize, but realistically with the school year ending in a few weeks, it seems unlikely we will be able to get what we want up and running,” says King, who adds that her queries to public health authorities about other efforts have come up empty. “There is some data collection happening in children, but it’s not focused around schools or, as far as I know, will not answer questions around transmission.”

Because children rarely suffer severe symptoms of COVID-19, pediatricians in several countries have called for schools to reopen. But a key question remains: Because people with mild symptoms can be extremely infectious and frequently spark large clusters of infections, could schools also be a source of COVID-19 outbreaks, possibly driven by children who feel fine but can pass the virus to each other, their teachers, and their families?

In Sweden, they have had a rare opportunity to understand [school] transmission chains better. But you can’t find what you don’t look for.

Anita Cicero, Johns Hopkins University Bloomberg School of Public Health

Health officials and researchers around the world are scrambling to answer that question. Key to that effort is tracing whether infected children spread the virus to people they’ve been in contact with. “I’m concerned that there may be a rush to judgment that asymptomatic school children aren’t spreading COVID-19 to adults,” says Anita Cicero, an expert in pandemic response policy at Johns Hopkins University’s Bloomberg School of Public Health. “In Sweden, they have had a rare opportunity to understand [school] transmission chains better. But you can’t find what you don’t look for. The U.S. and other countries with closed schools would certainly benefit from that research.”

Emma Frans, a clinical epidemiologist at KI who also writes a regular newspaper column on science and health, says Sweden’s overall goal during the pandemic has not been to eliminate transmission completely, but to prevent the health system from becoming overburdened and to protect the elderly. (It has succeeded at the former but not the latter: Sweden has suffered very high mortality among nursing home residents.) Regarding schools, Frans says, “Most people in Sweden are quite happy with [them] being open.” She acknowledges the lack of data is a missed opportunity. With Sweden’s centralized health system and extensive records, “it would have been possible” to track cases fairly easily had there been more testing.

But KI pediatrician and clinical epidemiologist Jonas Ludvigsson, who has published two review articles about COVID-19 in children, thinks tracing infected people’s contacts is of little use at this point in the epidemic. “The virus is so widespread in society that responsible people do not think it is a good idea to trace individuals. We only test symptomatic individuals. I agree with that,” he wrote in response to Science asking whether researchers were tracking school outbreaks.

Ludvigsson added that Swedish privacy laws allow health care personnel and school officials to notify parents and school staff about an infection only “if a person’s life is at risk.” Because severe complications from the new coronavirus are so rare in children, that does not apply to cases of COVID-19, he says. “Consider if your own child … had COVID-19,” he wrote. “None of the kids will want to play with a child who has COVID-19, even if most kids will have no symptoms or only ‘some fever and a cough.’”

In a review paper published 19 May in Acta Paediatrica, Ludvigsson concluded that children are “unlikely to be the main drivers” of COVID-19 spread. He cited case studies from France and Australia but wrote that, “So far there have been no reports of COVID-19 outbreaks in Swedish schools,” citing “personal communication” from Anders Tegnell, Sweden’s state epidemiologist, on 12 May. “This supports the argument that asymptomatic children attending schools are unlikely to spread the disease,” Ludvigsson wrote.

However, a scan of Swedish newspapers makes clear that school outbreaks have occurred. In the town of Skellefteå, a teacher died and 18 of 76 staff tested positive at a school with about 500 students in preschool through ninth grade. The school closed for 2 weeks because so many staff were sick, but students were not tested for the virus. In Uppsala, staff protested when school officials, citing patient privacy rules, declined to notify families or staff that a teacher had tested positive. No contact tracing was done at the school. At least two staff members at other schools have died, but those schools remained open and no one attempted to trace the spread of the disease there. When asked about these cases, Ludvigsson said he was unaware of them. He did not respond to a query about whether he would amend the review article to include them.

An indirect clue about schools’ role in spread might come from antibody studies. On 19 May, the Swedish Public Health Agency announced preliminary results from antibody surveys of 1100 people from nine regions. They reported that antibody prevalence in children and teenagers was 4.7%, compared with 6.7% in adults age 20 to 64 and 2.7% in 65- to 70-year-olds. The relatively high rate in children suggests there may have been significant spread in schools. The agency did not provide more specific data to distinguish between younger children and those in high schools and universities, which have switched to remote teaching.

The missed opportunity in Sweden is a wake-up call, King says: “We need ready-to-implement protocols for basic epidemiology during these situations.” Studies now underway in other European countries may soon provide more clues. And Cicero and colleagues issued a call last week to “fill in the blanks” in the understanding of U.S. schools’ role in the pandemic. “We need a national mandate to prioritize and quickly fund research to answer these scientific questions,” they wrote. “As schools reopen, [computer] models are not sufficient to determine the actual risk to school-aged children and the teachers and caregivers in their lives.”

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