The heated debate around opening schools just got some new evidence: if we open schools, there will be new clusters of infections, South Korean researchers warn.

So far, South Korea’s response to the pandemic has been exemplary. From being one of the first outbreak hotspots to becoming a leader in testing and having only double-digit cases for the past three months, South Korea has offered a remarkably efficient example of how to deal with a pandemic.

The country has also been active in coronavirus research. In the latest study, a team of researchers analyzed how COVID-19 is spread among different age groups.

Contact tracing offers valuable information

South Korea is one of the few countries that truly do contact tracing for coronavirus cases — and it’s very effective. In the study, researchers used contact tracing to identify 5,706 people who reported coronavirus symptoms between January and March, when schools were closed.

They traced 59,073 contacts of these cases, testing the household contacts of each patient, regardless of symptoms. They also tested contacts outside of the household, but only if they were symptomatic. There are some limitations to this approach (for instance not knowing who in a household is the first to be infected), but this approach can shed light on how the disease was spread through this community

What they found

Out of the total 10,592 household contacts who were tested, 11.8% had COVID-19. This is somewhat positive news since it means that the majority of household people did not contract the disease. Out of 48,481 nonhousehold contacts, 1.9% had COVID-19. The researchers found that personal protective measures and social distancing substantially reduce the likelihood of transmission.

When it comes to children between 0 and 9 years old, the risk of transmission was very low. Children in this age group were half as likely as adults to spread the virus. It’s not exactly clear why this happens, but it could be because children, in general, exhale less air (and therefore fewer viral particles), because they exhale air closer to the ground, making it less likely for other people to breathe it in, or because they have fewer ACE inhibitors.

But when it comes to teenagers (aged 10 to19), they were just as likely as adults to spread the virus, both to adults and their peers.

This goes against the idea that all kids are shielded from the disease and suggests that if schools were to reopen, this would lead to localized clusters both among children and the adults who are near them.

“We showed that household transmission of SARS-CoV-2 was high if the index patient was 10–19 years of age. In the current mitigation strategy that includes physical distancing, optimizing the likelihood of reducing individual, family, and community disease is important. Implementation of public health recommendations, including hand and respiratory hygiene, should be encouraged to reduce transmission of SARS-CoV-2 within affected households,” the authors write.

Now what?

South Korea adopted a rigorous contact-tracing program, including both epidemiological data and large databases (global positioning system, credit card transactions, and closed-circuit television). This approach is extremely valuable, especially since it would be hard or impossible to replicate in most places (it wouldn’t even be legal in the EU, for instance). The findings, while far from definitive, carry important lessons for the entire world.

Many countries, including the US, are struggling to figure out whether to reopen schools. Children in general seem more resilient to the disease, but apparently, when they do get it, they can pass it on with ease.

It’s important to note that researchers only traced children who felt sick. The transmission rates for asymptomatic cases remains unknown, and overall, children are less likely than adults to develop symptoms. It is unclear if asymptomatic children are also less likely to pass the disease.

However, it is becoming increasingly clear that opening schools will lead to clusters of infections. The idea that schools can be kept coronavirus-free while the virus is still at large in the area seems unlikely, although other studies have suggested that schools may still show resilience.

Whether or not this risk outweighs the downsides of keeping schools closed is a different discussion. For now, there is much uncertainty and opening schools seems bound to come at a cost. In a recent poll, 71% of Americans said it would be risky to send their kids to school.

Ultimately, the decision will be taken by politicians. We can only hope they also look at the science.

Read the study here.