Masks reduce Covid contagion in schools, study shows


Masks have been a cultural talking point since the beginning of the pandemic, and the mandatory use of them in schools is especially incendiary. Critics argue that there is no strong evidence to prove that masks slow the spread of Covid-19 and that, in any case, children were not wearing the right types of masks or were not wearing them properly.

Now, research details a so-called “natural experiment” that took place when all but two school districts in the greater Boston area lifted mask requirements in the spring. The researchers took the opportunity to make a direct comparison of the spread of Covid-19 in schools with and without masks.

Conclusion: Mask use was associated with a significantly reduced number of Covid-19 cases in schools.

Infection rates were lower among masked students — even in Boston Public Schools, where many buildings are old and lack good ventilation systems, classrooms are overcrowded, and students often belong to at-risk communities — than than among unmasked students attending newer schools in communities like Cambridge and Newton.

The study, by scientists at Harvard’s T.H. Chan School of Public Health and Massachusetts General Hospital, the Boston University School of Public Health and the Boston Public Health Commission, was published Wednesday in the The New England Journal of Medicine.

The data should help dispel misinformation about the effectiveness of general mask-wear requirements to curb viral transmission in schools, said Julia Raifman, assistant professor at the Boston University School of Public Health and author of an editorial accompanying the new study.

“As recently as this summer, people were saying, ‘Oh, Covid doesn’t spread in schools,’ and there was a misconception that kids don’t get Covid,” said Raifman, who was not involved in the new research. “But what we see in the study is that Covid spreads in schools, spreads back home and spreads to teachers.”

The study did not specify the types of masks used by children, suggesting that any type was at least somewhat protective, he added.

“This study shows that if people are wearing masks as a group, it decreases transmission to the entire population and reduces school and teacher absences,” Raifman said.

Even after the Centers for Disease Control and Prevention lifted the requirement for masks in schools last year, many states maintained the requirement. Massachusetts, along with 18 other states and Washington, D.C., maintained the use of masks in public schools at the start of the 2021-22 school year, but canceled the policy in February.

Until then, trends in the incidence of Covid-19 were similar across school districts in the greater Boston area. After lifting the obligation to wear masks, the state required districts to continue reporting all Covid-19 cases among students and staff, and provided funding and support services for testing.

The researchers involved in the study used that data to track Covid-19 cases each week across 72 school districts, comparing the two who kept masks on for 15 weeks — Boston and Chelsea — with another 70 who lifted that requirement at different times.

The suspension of mandatory mask use was associated with an additional 44.9 cases of Covid-19 per 1,000 students and staff, corresponding to an estimated 11,901 cases during the 15-week period, the scientists concluded.

“We’ve seen sustained and increased rates of Covid incidence consistently in schools that have lifted the mask requirement,” said Tori L. Cowger, the study’s first author and a postdoctoral fellow at the Harvard School of Public Health.

At 12 weeks out of the 15-week period, “we observed an increase in incidence that was statistically significant,” he added.

But only 1 in 3 cases of Covid-19 in schools where mask-wearing was lifted could be attributed to the change in policy; 4 out of 10 cases among employees were attributable to the policy change, she said.

Because people who tested positive were instructed to self-isolate for at least five days, the additional cases led to at least 17,500 missed school days for students and 6,500 missed school days for staff, the study calculated.

Opponents of wearing masks in schools have criticized the data on their effectiveness, but have also raised other concerns.

Masks can cause communication problems and delays in speech development, can be particularly burdensome for children with learning disabilities, and make it difficult to read or communicate emotional expressions, critics said.

And many adults, as well as children, find masks very uncomfortable, especially when worn throughout the school day.

Dr Tracy Beth Hoeg, a public health researcher and a fierce critic of masks in schools, noted that the new study is observational rather than a randomized controlled trial. So, she said, it can point to a correlation, but not prove a causal relationship between mandatory masking and a lower incidence of Covid-19.

Shira Doron, an infectious disease physician at Tufts Medical Center in Boston, who has criticized mandatory mask use in schools in the past, said the new study is just a publication and that the medical literature on mandatory mask use in schools it’s mixed.

Schools did not abandon mask policies because they were ineffective at containing viral transmission, Doron said, but because they could lead to other complications.

“Children with language learning difficulties are having trouble understanding their teachers and peers,” said Doron. “Children with speech difficulties are having trouble being understood to the point of withdrawing. Children and staff with hearing difficulties are having trouble communicating and understanding each other.”

She added: “Even teachers who have chosen to continue wearing a mask prefer that there is no obligation, so they don’t have to deal with discipline all day.”

But a Boston parent group, BPS Families for Covid Safety, has already called for the reinstatement of universal mask use in schools, saying the new study provides evidence that the practice protects against illness and lost learning days in a district where vaccination rates are relatively low and families come from communities that have suffered disproportionately during the pandemic.

Translated by Luiz Roberto M. Gonçalves

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