Routinely testing school children and staff for the coronavirus is unlikely to add much preventive benefit when community transmission is under control and safety measures are in place, a Seattle-based disease modeling group’s report says.

The findings, released Thursday, are good news for districts in communities with low coronavirus levels.  The study hints that a lack of coronavirus tests in schools shouldn’t be a barrier to bringing students back to buildings. 

“There isn’t that much additional impact that you get by doing the diagnostic screening,” said Dan Klein, who led the research and is a senior research manager at the Institute for Disease Modeling (IDM). 

The role of schools in spreading the virus that causes COVID-19 is still unclear, but the Washington state Department of Health (DOH) has said that early data is encouraging and suggests some schools can reopen buildings safely. On Thursday, Lacy Fehrenbach, the deputy secretary of health for COVID-19 response at the state health department, said DOH has logged 42 coronavirus outbreaks in schools — involving a total of 110 people — since the start of the pandemic. 

An outbreak includes two or more cases among staff or students over a two-week period, with evidence that transmission happened on school grounds. Only four of the recorded school outbreaks included more than five people, Fehrenbach said. Of those, three outbreaks were in places with high coronavirus incidence.

The IDM report suggests that testing would be more useful in areas where schools are a “significant source of infections,” such as places where coronavirus incidence is high in the community, as are many counties in Washington state. Tests would also be useful when schools can’t or won’t take safety precautions, the study says.


The finding also highlights the effectiveness of measures such as mandating masks and social distancing in classrooms, which are required in Washington schools that reopen.

And it comes on the same day that DOH officials said they intend to set aside 1 million COVID-19 tests for schools. The federal government is shipping testing kits to Washington weekly, officials say, with 2.3 million total kits expected by December. 

The new IDM report will guide DOH’s decision-making as it distributes these tests to school sites, Fehrenbach said in a call with reporters on Thursday. Fehrenbach didn’t elaborate on whether the state would prioritize regions with high incidence, but did say that at least one such county, Okanogan, was already using tests at some schools. More counties are expected to roll out testing soon, she added.

In King County, most public school children are unlikely to return to school buildings until next year. Bellevue, Seattle and several other districts have delayed reopening as coronavirus counts have soared. In late October, Public Health – Seattle & King County officials said they had no plans to “directly support testing in schools.” Elsewhere, New York City and Los Angeles are implementing limited testing at schools.

The new report is based on King County coronavirus data from October and relies on a mathematical model developed by IDM that uses demographic information, disease data and contact patterns to predict how reopening schools would affect coronavirus spread. 

Klein and his colleagues simulated different scenarios for school reopening — in-person and hybrid, for example — and predicted how various coronavirus testing strategies would help detect coronavirus and prevent its spread.


The modeling has several limitations. It uses King County data from several weeks ago, when coronavirus incidence was far lower than today. It also assumes that infection rates are stable — not trending upward, as they are now. Certain coronavirus tests — such as rapid antigen tests, the type schools may receive — are less sensitive than other tests, and it’s unclear how well they would perform in a school setting. 

But the findings do add weight to evidence suggesting that safety precautions, like social distancing and mask-wearing, will keep transmission at bay. 

The study provides “convincing evidence that those measures alone, especially with a hybrid model or a K-5 model, would really produce very few additional cases,” said Brandon Guthrie, who was not involved in the research and is assistant professor of global health and epidemiology at the University of Washington.

Testing in schools may be one route to building confidence in the community when districts eventually open buildings, Guthrie said. But broad-scale testing — especially in places where coronavirus incidence is low, and tests are less likely to pick up positive cases — would be an expensive endeavor.

If “the only way that people would feel safe opening schools is if you could detect every single case within ‘X’ number of days,” he said, then schools could calculate how many tests they would need to conduct. “And then you can say, is it worth that cost?”