A Huge Covid-19 Natural Experiment Is Underway—in Classrooms

For parents and teachers, the reopening of schools has been a chaotic mess. Guidelines and procedures seem to change daily. Classroom policies or even whether in-person learning occurs at all depends on where you live and often the politics of who sits in the governor’s mansion. But for epidemiologists, this fall is proving to be a scientific bonanza of sorts. “The opening of schools is a tremendous opportunity for natural experiments to understand transmission,” says Tina Hartert, a pediatric epidemiologist at Vanderbilt University Medical Center.

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Researchers like Hartert want to know how effectively this coronavirus spreads, how much of a risk children and teenagers pose for transmitting the virus, and whether any of the measures that schools are taking right now—from staggered schedules to new ventilation systems to chemically disinfecting the desks—make a difference.

While existing studies have examined these questions, most were conducted last spring when schools were closed and children were at home. Those that did look at schools that had reopened, in Germany and Israel for example, had small sample sizes, Hastert says. “We are not confident looking at the whole body of literature in making claims of children’s role in transmission as compared with adults,” says Hartert, who is also coordinating a nationwide National Institutes of Health-funded study examining novel coronavirus spread among households.

The study, known as Human Epidemiology and Response to SARS-CoV-2 (Heros), also will help determine what percentage of children infected with the virus develop symptoms of the disease, and compare the infection rates among children who have asthma or allergic conditions with those of kids who do not. More than 1,900 households in 12 US cities have been enrolled in the study, and Hartert hopes to have some preliminary data in early 2021.

Hartert is specifically examining how the virus travels throughout families. She says she wants to see a similar study of how the virus might spread through a school. “It’s not as simple as only studying the school,” Hartert says. “The school building is only one network that students interface with when they leave class, get on buses, and go home.”

Data experts say that designing studies about school transmission or about mitigation measures isn’t so easy. For one thing, in school districts where most parents are unable to work from home or lack access to a computer and the internet, administrators may have an incentive to keep their schools open despite the risk from the virus, says Zoe McLaren, professor of health policy at the University of Maryland, Baltimore County.

“In communities where the students are relatively disadvantaged, they are likely to go back to school, because the students will likely fall further behind,” McClaren says. “If there are outbreaks, they are more poorly resourced. If they had money for better ventilation systems and to have smaller class sizes, they would have been able to do it safely.”

Even if researchers can take into account the economic disparities among school districts, any school study will have to conduct a lot of Covid-19 diagnostic tests among the students, teachers, and staff over a long period of time to track the progress of the virus. They will also have to run a detailed accounting of each person that an infected student or teacher meets, a strategy known as contact tracing, which is both labor-intensive and expensive to do.

In tracking respiratory diseases like the coronavirus, “you can’t tell as easily what has happened after the fact,” says Dimitri Christakis, a pediatrician at Seattle Children’s Research Institute. “That’s why you need to be testing children, so you know that they came to school without Covid, that five kids now have Covid-19, and then also contact-trace with their families. You have to have the infrastructure in place, otherwise it becomes very difficult or even impossible to trace.”


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