Ventilation and surveillance testing can help keep U.S. schools open in the fall, new studies suggest

Several Covid-19 mitigation measures — including improving ventilation, requiring adults to wear face masks and conducting frequent surveillance testing — can help schools stay open and students remain safe, two new studies suggest.

The studies, which were published on Friday, come as many school districts are drawing up their plans for the fall. They also follow the Centers for Disease Control and Prevention guidance that all schools teaching students from kindergarten through grade 12 should continue to have mask-wearing policies through the end of the 2020-21 school year, after the agency’s recent move to allow for vaccinated people to forgo wearing masks indoors. The agency also kept in place its suggestions to observe physical distancing and to test for coronavirus infections.

In one of the new studies, researchers from the C.D.C. and the Georgia Department of Public Health surveyed 169 elementary schools in Georgia that offered in-person learning in the fall. The group asked the schools about their pandemic responses and collected data on the coronavirus cases detected between Nov. 16 and Dec. 11, before Covid-19 vaccines were available in the United States.

The researchers found that the incidence of the virus was 35 percent lower in schools that had improved their ventilation — by opening windows or doors, or using fans — than in schools that did not adopt these practices. In schools that combined better ventilation with air filtration — through the use of HEPA filters, for instance — case rates were 48 percent lower.

Requiring all teachers and staff members to wear masks reduced the incidence of the virus by 37 percent, the researchers found. Schools that required students to wear masks had a 21-percent-lower incidence of the virus, but that reduction was not statistically significant, the scientists found. That may be a result of the fact that adults are more likely to transmit the virus than children are, or simply because of a small sample size.

“Because universal and correct use of masks can reduce SARS-CoV-2 transmission and is a relatively low-cost and easily implemented strategy, findings in this report suggest universal and correct mask use is an important Covid-19 prevention strategy in schools as part of a multicomponent approach,” the researchers write, referring to the virus that causes Covid-19.

A second study, led by researchers at the Utah Department of Health and the University of Utah, tracked the implementation of two coronavirus screening programs in the state’s schools. One program, which was established in January 2021, allowed schools with outbreaks to conduct schoolwide testing instead of shifting to remote learning.

“Schools could either do what they had been doing in the fall, which was switch to remote for a two-week period to interrupt transmission chains, or it could test everyone,” said Dr. Adam Hersh, one of the study’s authors and an expert in pediatric infectious diseases at the University of Utah. “And those who tested negative could return to in-person learning and those who tested positive obviously would be isolated.”

A second testing program required students to be tested for the coronavirus every 14 days in order to participate in sports or other extracurricular activities. Both initiatives relied on rapid antigen tests, which are less sensitive, but cheaper and faster, than the standard P.C.R. tests.

This year, between Jan. 4 and March 20, 28 high schools in the state reported sizable outbreaks. Fifteen schools moved to remote instruction for two weeks, while the other 13 conducted surveillance testing instead. Of the 13,809 students who were tested as part of this screening, just 0.7 percent tested positive, the scientists reported. All 13 schools remained open.

“From a public health standpoint, it’s a huge success,” said Kendra Babitz, the coronavirus testing coordinator at the Utah Department of Health and one of the study’s authors. “Testing is and should be a mitigation strategy that schools are using to prevent transmission of SARS-CoV-2 in the school setting,” she added.

Over the course of the winter, 95 percent of school athletic events took place as scheduled, the researchers found, although they did not compare that figure with a control group of schools without screening programs. “That’s in range with what happens in normal season,” Dr. Hersh said. “The show was able to go on.”