Safe School Reopening in the COVID-19 Pandemic

Reviewed by Zachary Willis, MD, MPH; UNC Health

The ABC Science Collaborative previously demonstrated that public schools in North Carolina, implementing recommended mitigation strategies, could largely prevent in-school transmission of SARS-CoV-2 during a period of relatively low community transmission (fall 2020). Here, they update their analysis covering the winter of 2020-21 (late October through end of February), including the winter surge in North Carolina. Out of 4,969 community-acquired COVID-19 cases with 26,000 close contacts, there were 209 school-acquired COVID-19 infections – less than 1% of all close contacts. In high schools, most cases of secondary transmission were associated with athletic settings rather than the classroom. It should be noted that the participating schools used hybrid models in PreK through fifth grade to decrease density, a strategy that is no longer widely used, and that testing of asymptomatic contacts was not performed systematically. Nonetheless, the authors provide detailed evidence about the effects of reasonable COVID-19 mitigation strategies.

Separately, researchers in Arizona examined the effect of school mask mandates in nearly one thousand schools in two large counties in July and August of 2021. Arizona mandates reporting of school outbreaks, defined as two or more confirmed COVID-19 case within a 14-day period. A mask requirement was defined as requiring all persons to wear a mask indoors in school; individual schools were classified as having no mask requirement, a mask requirement present at the start of the school year (“early”), or a mask requirement implemented after the start of the school year (“late”). Only 8% of schools with an early mask requirement had a school-related outbreak, compared to 24% of those with no requirement, translating to 3.5 times greater odds in schools with no requirement in the adjusted analysis.

In the first year-plus of the COVID-19 pandemic, three distinct approaches to in-person schooling emerged: 1) no in-person school; 2) in-person school with strong mitigation policies; and 3) full in-person school with minimal or no mitigation efforts. By the fall of 2021, almost all schools had reopened fully, but there are vast differences in COVID-19 prevention strategies. These new studies demonstrate that school can proceed safely if appropriate mitigation strategies are in place. Mask requirements are inexpensive and feasible: they do not require retrofitting of ventilation systems or reorganization of classrooms and schedules. More importantly, the best available evidence suggests that mask requirements are highly effective in preventing SARS-CoV-2 transmission in the school setting.


Zimmerman KO, Brookhart MA, Kalu IC, et al. Community SARS-CoV-2 Surge and Within-School Transmission. Pediatrics. 2021;148(4). doi:10.1542/peds.2021-052686

Jehn M. Association Between K–12 School Mask Policies and School-Associated COVID-19 Outbreaks — Maricopa and Pima Counties, Arizona, July–August 2021. MMWR Morb Mortal Wkly Rep. 2021;70. doi:10.15585/mmwr.mm7039e1

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