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Schools that kept mask mandates saw significantly fewer COVID-19 cases: study


Around 30 per cent of COVID-19 cases among students and staff in schools around Boston could possibly have been prevented if they hadn’t lifted their masking mandates, according to a new U.S. study.

Researchers looked at more than 70 school districts to compare those that had mask mandates with those that didn’t, and found that masking in schools was associated with significantly fewer COVID-19 cases.

School districts in the greater Boston area that lifted mask mandates last February saw an additional 44.9 COVID-19 cases per 1,000 students and staff across 15 weeks compared to schools that kept masking, according to the study.

This comes out to nearly 12,000 cases of COVID-19 connected to the lifting of mask mandates in this region, making up roughly 30 per cent of the cases at that time across all of the school districts.

When looking at only COVID-19 among staff, the impact of masking was even clearer: school districts with no mask requirements had an additional 81 cases per 1,000 staff members overall, with case rates nearly double that of schools that kept masking.

“Our study shows that universal masking is an important strategy to reduce transmission in schools and one that should be considered in mitigation planning to keep students and staff healthier and minimize loss of in-person school days,” Tori Cowger, corresponding author and Health and Human Rights fellow in the FXB Center for Health and Human Rights at Harvard Chan School, said in a press release.

“Our results also suggest that universal masking may be an important tool for mitigating structural inequities that have led to unequal conditions in schools and differential risk of severe COVID-19, educational disruptions, and health and economic effects of secondary transmission to household members.”

This study comes amid calls from health experts and officials for Canadians to start wearing masks again if they’d stopped. Ontario Premier Doug Ford advised the public on Sunday to "wear a mask every time possible,” and the province’s top doctor is set to recommend masking on Monday — but it’s unclear if this advice will lead to a provincial mask mandate in schools and businesses.

Mask mandates have all but vanished in many areas of Canada this year, despite COVID-19 hospitalizations and deaths occurring at higher rates than in 2021.

As of Nov. 7, there were 6,083 people hospitalized with COVID-19 in Canada. Last year, the highest number of people hospitalized with COVID-19 at one time was 4,930, according to the federal government.


Numerous studies have shown that wearing a mask in public indoor spaces can provide greater protection against COVID-19 and other airborne viruses, but not many studies have been able to directly compare the results of schools having mask mandates to those that removed them.

Massachusetts rescinded their universal masking mandate for public schools in February 2022, and the vast majority of schools responded by dropping their mask mandates.

Only two school districts — Boston and Chelsea — decided to keep their masking requirements in place through June 2022, providing a perfect opportunity for researchers to compare the incidence rate between schools that mandated masks and those that didn’t.

The resulting study, published earlier this week in the New England Journal of Medicine, tracked 72 school districts in the greater Boston area for 15 weeks after the statewide mask mandate was lifted.

This covered more than 294,000 students and 46,500 staff.

Prior to the lifting of the statewide masking requirement, the trends of COVID-19 cases were relatively similar across all of the school districts.

Only after some schools stopped requiring masks and other didn’t did a new trend begin to emerge.

Graphs of the COVID-19 incidence rate in the included school districts show that cases increased across the board in all schools as case levels rose in the community. But schools that lifted mask requirements saw a much bigger increase in cases than those that didn’t.

Forty-six of the school districts lifted masking requirements during the first school week after the statewide mandate was lifted, while 17 districts lifted their mandates in the second week, followed by seven districts in the third week. Only two school districts kept their masking requirements to the end of the school year.

Schools that lifted their mask mandate in the first week had the highest COVID-19 incidence level among staff of all districts, while schools that lifted their masking mandate in the second week had the highest incidence level among students by themselves, as well as students and staff combined.

The two districts that maintained mask mandates reached around 10 weekly cases of COVID-19 per 100 students and staff during their highest peak of cases in late May.

At the same time, the other districts were experiencing 15-25 weekly cases per 100 students, around 50-150 per cent higher.

There was also a clear toll in terms of learning hours for students attending a school without masking requirements. Researchers calculated that because those who had a positive COVID-19 test were required to quarantine at home for at least five days, the additional cases associated with a lack of masking mandates translated to at least 17,500 missed days of school for children and 6,500 missed days for staff during those 15 weeks.

“This study provides clear support for the importance of universal masking to reduce transmission of COVID-19 in school settings, especially when community COVID levels are high,” Eleanor Murray, assistant professor of epidemiology at Boston University School of Public Health and study co-author, said in the release. “Masking reduces COVID-19 transmission in schools in an equitable and easy to implement way and should be part of any layered mitigation strategy.”

Researchers also noted that the school districts that chose to keep their masking requirements tended to have older school buildings that may have had poorer ventilation or fewer windows, had more students per class, and generally served lower-income communities, stating that universal masking can help make up some of the inequalities that poorer students may already face. Top Stories

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