Lifting universal masking in schools associated with new Covid-19 cases

The lifting of masking requirements in school districts outside of Boston in February 2022 was associated with an additional 44.9 COVID-19 cases per 1,000 students and staff in the 15 weeks after the statewide masking policy was rescinded. This represented nearly 12,000 total COVID-19 cases or 30% of all cases in those school districts that unmasked during that time, according to a new study led by Harvard T.H. Chan School of Public Health, the Boston Public Health Commission, and Boston University School of Public Health.

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. 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."

Tori Cowger, corresponding author and Health and Human Rights fellow in the FXB Center for Health and Human Rights at Harvard Chan School

The study was published online in the New England Journal of Medicine, Nov. 9, 2022.

When Massachusetts rescinded its statewide universal masking policy earlier this year, many schools in the state, including those in the greater Boston area, lifted their requirements over the next several weeks. However, two school districts—Boston and Chelsea—maintained universal masking policies through June. That staggered lifting of masking requirements gave the researchers the unique opportunity to examine the impact of lifting those requirements on the incidence of COVID-19 among students and staff across 72 school districts in the greater Boston area.

The researchers found that before the statewide masking requirements were lifted, the trends in the incidence of COVID-19 observed in the Boston and Chelsea school districts were similar to the trends in the districts that later lifted masking requirements. After the statewide policy was rescinded, the trends diverged, with a substantially higher incidence observed in districts that lifted masking requirements compared to districts that maintained their masking requirements.

The findings also showed that the effect of school masking policies was greatest during periods when COVID-19 incidence was highest in surrounding cities and towns, suggesting that implementing universal masking policies during times of high transmission would be most effective.

"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," said study co-author Eleanor Murray, assistant professor of epidemiology at Boston University School of Public Health. "Masking reduces COVID-19 transmission in schools in an equitable and easy to implement way and should be part of any layered mitigation strategy."