Large-scale random testing and follow-up of contacts over time, which would give a more complete picture of who transmits the virus and how, has yet to be done in schools. In July, in the journal Emerging Infectious Diseases, researchers from the Korea Centers for Disease Control and Prevention published search results for more than 59,000 contacts of 5,706 coronavirus patients. Children under the age of 10 were found to transmit the virus much less than those aged 10 to 19, whose transmission rate was equivalent to that of adults. But only 3 percent of the patients in that initial cohort were 19 years old or younger, and the fact that they were evaluated probably means they had symptoms. It is still unclear how asymptomatic children, who are difficult to identify, can transmit the virus; It is also unclear if there are differences in transmission between the ages of 10 and 19.
“A lot of the data we get from different sources is confusing and doesn’t necessarily point in the same direction,” says Nicholas Davies, an epidemiologist at the London School of Hygiene & Tropical Medicine. He and his colleagues used a statistical method called Bayesian inference to test various hypotheses about children and Covid. These included the premises that children are infected but show no symptoms and that children are less susceptible to infection. Based on epidemiological data from China, Italy, Japan, Singapore, Canada, and South Korea, the researchers concluded that both premises were probably true, to some extent. Their findings, published in Nature Medicine in June, estimate that people under the age of 20 are about half as likely to be infected as older groups, and that among people 10 to 19 years old who contract the virus, only the 21 percent will have clinical symptoms. They could not make more precise age distinctions, or say how likely it is that one child will infect others.
Neither of these studies directly addresses the impact of reopening schools on the spread of Covid. In fact, when researchers from the University of Washington’s Departments of Global Health and Epidemiology began to compile a summary of models from 15 other countries to which the students returned, they found “very few” scientific publications on the subject and relied primarily on news reports. In almost all countries, they observed, schools adopted security measures, including face masks and social distancing. None of the countries (except Sweden, which kept many schools open) resumed classes before national infection rates had decreased significantly; There is no evidence to say what the result would be of opening schools in areas of the U.S. where the virus is emerging. In Germany, where infection rates were higher than in other European countries, the return of older students accompanied an increase in infections among themselves, but not among staff, according to a preprint led by researchers from the University of Manchester and Public Health England.
In Israel, students and staff wore masks after schools reopened in early May. But several weeks later, those rules were relaxed. According to Haaretz, the outbreaks began soon after, exposing thousands in schools to the infection, causing many of them to close again. “There is no clear cause and effect” between the removal of the masks and the shoots, says the lead author of the abstract, Brandon Guthrie, but it is “circumstantial evidence” that they offer some protection in the classroom. It also reveals how inapplicable the health orientation schools receive can be.
