Mandatory Masking Reduced Covid-19 Cases in Schools During Delta

Mandatory masking was associated with a 72 percent reduction of in-school Covid-19 cases, during the Delta surge.

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Schools with mandatory masking during the Delta surge had approximately 72 percent fewer cases of in-school transmission of SARS-CoV-2 compared with schools with optional or partial masking policies, according to an NIH-funded study.

The study included more than 1.1 million students and more than 157,000 staff attending in-person school across 9 states: North Carolina, Wisconsin, Missouri, California, Washington, Georgia, Tennessee, Kansas and Texas. The study, published in Pediatrics, is supported by NICHD and RADx-UP.

The study was conducted when Delta was the dominant variant and does not include data on school masking in preventing the spread of the Omicron variant. 

The study included 61 school districts (kindergarten through grade 12) that provided data from July 2021 through Dec. 13, 2021, a period encompassing the Delta surge and preceding the Omicron surge. 

In this study, most Covid-19 cases among students and staff were acquired from the community and approximately 10 percent of cases were acquired within school. The researchers found that for every 100 community-acquired cases, school districts with mandatory masking had approximately 7.3 cases of in-school infections, while optionally masked districts had 26.4 cases of in-school infections. 

In other words, school districts with optional masking had approximately 3.6 times the rate of in-school cases compared to schools with mandatory masking. 

The authors noted masking remains a critical preventive measure during high community infection rates with more transmissible variants, such as Delta and Omicron.