New study of North Carolina schools show wearing masks slows spread of COVID-19

Masking mandates in 20 North Carolina school districts resulted in lower COVID-19 infection rates among students and staff than reported rates of infection in the larger community, according to an ABC Science Collaboratives study published this week in The Journal of Pediatrics.  

The study included 783 K-12 schools representing 59,561 students and 11,854 staff members in 20 districts that held summer school or year-round school between June 14 and Aug. 13, a period when the Delta variant was fast becoming the dominant strain of the coronavirus.

Kanecia Zimmerman

“The findings of this study are extremely encouraging for the health and safety of students and staff attending schools where universal masking is in place,” said Dr. Kanecia Zimmerman, a Collaborative co-chair. “The Delta variant is more transmissible than previous ancestral variants, but transmission in schools can continue to be low with vaccination among those who are eligible, strict adherence to masking, and avoidance of pandemic fatigue.”

The Collaborative is coordinated by the Duke Clinical Research Institute at the Duke University School of Medicine. The initiative extends across 18 states. It connects scientists and physicians with school and community leaders to help understand the most current and relevant information about COVID-19.

School districts in the Collaborative’s analysis followed the NC Department of Health and Human Services (NCDHHS) StrongSchoolsNC Toolkit, which recommended, but did not require, at least three feet of physical distancing between people. The state mask mandate for K-12 settings was in effect during the study period.

Here’s what researchers had to say about the analysis:

During the study, there were 808 community-acquired cases reported vs. 64 school-acquired cases. The Delta variant has a reproductive number of about 7, meaning that, on average, in the community, one person infected with the Delta variant infects 7 others. However, in schools that implemented universal masking, for every 13 people who acquired COVID-19 outside of school, one person acquired COVID-19 within schools. As a result of COVID-19 exposure at school, 2,431 close contacts were quarantined, and 64 people acquired infections in schools, resulting in a secondary attack rate of 2.6%. This secondary attack rate is slightly higher than the secondary attack rate of approximately 1% that the ABC Science Collaborative found before the emergence of the Delta variant. This is likely due to the more infectious nature of the Delta variant.

The researchers said the study did not allow for a comparison to an unmasked setting because a statewide mask mandate was in place, but data from other schools without a mask mandate during July-August 2021 showed these schools were 3.5 times more likely to have school-associated COVID-19 outbreaks than the schools in this study that required masking.

The data from this study also highlight the importance of remaining vigilant during times throughout the school day when strict mask adherence may not be possible, the researchers said.

Daniel Benjamin

“Looking forward to the fall and winter, lunch and extracurricular activities will be areas that require additional attention to limit the transmission of COVID-19 within schools,” Dr.  Danny Benjamin, who also co-chairs the Collaborative. “As pediatricians and public health experts, we encourage schools to put mitigation strategies in place, such as vaccination, masking, and eating outside, to protect students and staff.”

The Collaborative is funded through grants from the National Center for Advancing Translational Sciences, the National Institutes of Health, and the Food and Drug Administration.

On Thursday, state health officials reported that there have been significantly fewer COVID-19 clusters in North Carolina school districts requiring masks compared to those that do not.

State Health Director Betsey Tilson told the State Board of Education that in three counties without a school mask mandate between Aug. 26 and Sept. 26, there were 17.2 clusters per 100 schools. In the 89 counties with “consistent” mask mandates, there was an average of 6.9 clusters per 100 schools, Tilson said. Thirty-five of the counties did not report a cluster.

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