More US school districts have dropped mask mandates in recent weeks as coronavirus cases plunged across the United States. But they remain a topic of debate among some students and their parents, and a study released Tuesday by the Centers for Disease Control and Prevention suggested that these mandates helped protect children and teachers from the coronavirus last fall.
The study, examining public school districts in Arkansas from August through October as the Delta variant spread, found that districts with full-face mask requirements had 23% lower coronavirus rates among students and teachers. staff members as districts without terms of reference.
It was unclear if the same would have been true once the Delta variant was overtaken by Omicron, which is more contagious and spreads quickly among children and adults.
The CDC has faced criticism from scientists in the past for overstating the benefits of school masking based on what some researchers described as a flawed study in Arizona. Some foreign studies have also found that mask mandates were not associated with lower rates of coronavirus in children.
But some scientists said the CDC’s latest study avoided the most serious methodological problems and strengthened the evidence of masks protecting some children from the coronavirus.
“It passes the smell test,” Louise-Anne McNutt, a former CDC epidemic intelligence officer and epidemiologist at the State University of New York at Albany, said of the study. “The masks’ impact estimates are consistent with other studies that show masks have a modest, but important, reduction in SARS-CoV-2 transmission.
The study compared coronavirus case rates among 233 districts in Arkansas. About a third of districts had full-face mask mandates, a fifth only required masks in certain settings or situations, and half had no mask policy.
It took into account staff and student vaccination rates and socio-economic status. It also adjusted coronavirus rates in the surrounding community — an attempt, the study authors said, to partly control the amount of testing taking place in a given part of the state. Dr McNutt, however, said the study would have benefited from more detail on statewide testing levels.
Districts with full mask mandates had lower coronavirus rates relative to case rates in the surrounding community than districts without the mandates, the study found. And among about two dozen districts that implemented mask mandates midway through the study period, case rates then fell more than might have been expected from changes in community case rates. at the same time, according to the study.
Partial mask policies did not show as strong an effect as full mask mandates.
The study did not consider schools’ prevention efforts beyond masking, such as ventilating classrooms. Jonathan Ketcham, a health care economist at Arizona State University, said that could be a “significant flaw in the study itself.”
Jason Abaluck, an economics professor at Yale University’s School of Management who helped lead a large masking trial in Bangladesh, also warned that schools with mask mandates might have differed from those without. There were no other ways, such as respecting distancing measures. He said the study could have better matched neighboring schools with different masking policies to study their effects.
But Dr. Abaluck said the CDC study was an improvement over previous research.
“This study and the broader literature on masking suggests that in places with very high hospitalizations and deaths, the benefits of mask-wearing in schools can be substantial,” he said.
Still, he noted that masks can cause discomfort and make it more difficult for children to communicate. “Determining how severe an outbreak must be to justify mask mandates in schools,” he said, “requires making best guesses about costs, which remain highly uncertain given the existing evidence.”