Universal Masking in Schools is Shown to Reduce Spread of COVID-19

School districts that required masking saw lower rates of COVID-19 transmission within schools last fall compared to those with optional masking policies, according to a study by the ABC Science Collaborative.

The ABC Science Collaborative

The study, published online on March 9 in the journal Pediatrics, found that school districts with universal masking were less likely to experience COVID-19 spreading in their schools when compared to school districts with optional masking (masked schools had 72% less within-school spread compared to unmasked schools). After taking into account the size of the school districts and how many weeks the districts contributed data, masked schools saw up to 87% less transmission.

The study is the first to compare within-school COVID-19 spread from a large population of American schools that mask with those that don’t. The study included 61 school districts, more than 3,000 schools, and more than 1.1 million students and adults from across nine states.

Of the 61 districts in the study, six (10%) had optional masking and nine (15%) had partial masking policies, meaning their masking policies changed at some point during the study or did not apply to all grade levels. The remaining 46 districts (75%) had required masking over the course of the study.

School districts reported their practices surrounding masking, quarantine, and lunch period, and reported weekly infection data from July 26, 2021 to Dec. 13, 2021. That time period occurred during the Delta variant surge and concluded in the beginning weeks of the Omicron variant surge.

During the study period, participating districts had 40,601 community-acquired infections (36,032 among students, 4,569 among staff) and 3,085 in-school infections (2,844 among students, 241 among staff).

Districts that were fully masked had lower predicted in-school infections per community-acquired infection than districts that had an optional masking policy. Classification of community-acquired and in-school infections were determined by school health staff in collaboration with the local health department.

“The results of this study clearly show that universal masking reduces school transmission of COVID-19 when compared to optional masking, a finding that is consistent with earlier data,” said Danny Benjamin, MD, PhD, co-chair of the ABC Science Collaborative and distinguished professor in the Department of Pediatrics at Duke University School of Medicine.

“As more students have returned to school, masking and vaccination of children 5 years and older have remained the most practical and effective mitigation strategies to keeping students healthy and learning in-person,” Benjamin said.

Kanecia Zimmerman, MD, MPH

The study gave participating school districts tools for monitoring the success of their mitigation measures and evaluating policies based on the needs of their communities.

“Maintaining in-person instruction is critical for children,” said Kanecia Zimmerman, MD, co-chair of the ABC Science Collaborative and associate professor of pediatrics at Duke. “Providing districts with the ability to monitor transmission data in real time and in response to changing policies allows them to shape their mitigation efforts during an evolving pandemic.

“The findings in this study are important,” Zimmerman said. “Especially in times with higher community infection rates and more transmissible variants, masking is a critical safety effort to support continued, in-person education.”