THE BEST MASK STUDY YET

School districts across the nation have implemented mask mandates for children in the hope of reducing COVID-19 transmission, but the impact of school-based mask mandates on COVID-19 transmission in children is not fully established. While observational studies of school mask mandates have had conflicting results, randomized studies have failed to detect an impact of masking on participants under 50 years of age [1-6]. Here we report the results of a natural experiment in two large K-12 school districts in Fargo, North Dakota, Fargo Public Schools (FPS) and West Fargo Public Schools (WF), to estimate the association between school mask mandates and COVID-19 infections. Our study population is unique because the districts are adjacent to each other in the same county and have similar student demographics, COVID-19 mitigation policies and staff vaccination rates. At the start of the Fall 2021 semester, FPS mandated masks and WF did not. On January 17, 2022, FPS also moved to a mask optional policy, creating a unique natural experiment to study school-based mask mandates.