Mandatory masking in schools reduced COVID-19 cases

The study examined how masking policies affect the spread of COVID-19 within schools. wavebreakmedia / Shutterstock

SARS-CoV-2, the virus that causes COVID-19, most commonly spreads from person to person through respiratory droplets. These droplets travel through the air when people cough, sneeze, or talk. Studies show that masks reduce the release of droplets when worn over the nose and mouth.

While masks can prevent individuals from getting or spreading COVID-19, it can be difficult to assess how masking policies affect virus transmission in populations. In real-world situations, masking strategies are affected by many factors. For example, people wear different types of masks. Some don’t comply with masking policies, and others don’t wear masks properly.

Despite these challenges, studies have found that masking policies help to reduce the spread of COVID-19. Because of the importance of in-person childhood education, researchers want to know how masking policies affect transmission within schools.

To find out, a research team led by Drs. Kanecia Zimmerman and Danny Benjamin at Duke University studied 61 school districts across nine states. In all, the districts had more than 1.1 million students, from kindergarten through grade 12, and 157,000 staff. School health staff, in collaboration with local public health departments, tracked infections and reported which were acquired in the community and which in schools.

The districts provided data from late July through mid-December of 2021. Six of the districts had optional masking policies during this period; nine had partial masking (policies that changed during the study or only applied to certain grade levels); and 46 required masking.

The study was supported by NIH’s Rapid Acceleration of Diagnostics – Underserved Populations (RADx-UP) program and Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). Results appeared in Pediatrics on March 9, 2022.

In total, the team recorded more than 40,000 infections acquired in the community (36,000 among students) and about 3,100 infections acquired in school (2,800 among students). Compared to optional masking, mandatory masking was associated with a 72% reduction of in-school COVID-19 cases. 

School districts with mandatory masking had 7.3 cases of in-school infection for every 100 community-acquired cases. Districts with optional masking had 26.4 cases of in-school infection for every 100 community-acquired cases. The results were similar when the researchers adjusted for district size and weeks of reporting data.

This study was conducted when Delta was the dominant variant. The team didn’t obtain data on how school masking affected the spread of Omicron. However, based on all available data, the CDC recommends indoor masking whenever there are high community levels of COVID-19.

“These findings show that school masking remains a critical preventive measure in times with high community infection rates, as we observed with Omicron, or if a variant emerges that escapes immunity,” Benjamin says.

—by Harrison Wein, Ph.D.