In conjunction with North Carolina, the ABC Science Collaborative collected data from more than one million students and staff members in the state’s schools from March to June 2021. Certain school districts in North Carolina were required, by bipartisan legislation, to submit infection data to the ABC Science Collaborative as a trusted third party.

During that time, more than 7,000 children and adults acquired the coronavirus and attended school while infectious. Because of close contact with those cases, more than 40,000 people required quarantine. Through contact tracing and testing, however, we found only 363 additional children and adults acquired the coronavirus. We believe this low rate of transmission occurred because of the mask-on-mask school environment: Both the infected person and the close contact wore masks. Schools provided this protection without expensive screening tests for the coronavirus or massive overhauls in ventilation systems.

Because North Carolina had a mask mandate for all K-12 schools, we could not compare masked schools to unmasked schools. To understand the preventive impact masks can have, we looked outside North Carolina for comparisons. Data from our research and from studies conducted in Utah, Missouri and Wisconsin shows that school transmission rates of coronavirus were low when schools enforced mask mandates.