A study by Cowger and colleagues appearing in the Nov. 9 issue of the NEJM provides new evidence that the removal of universal school masking policies in Massachusetts was associated with an increased incidence of Covid-19.
From the accompanying editorial by Raifman and Green:
“The study used difference-in-differences methods, a rigorous form of causal inference for policies that are infeasible or unethical to assess in a randomized trial. During a 15-week period (March to June 2022), Covid-19 cases in school districts that had ended universal school masking policies (70 districts for most of the 15-week period) were compared with cases in school districts that sustained universal masking policies (2 districts for most of the 15-week period). The removal of universal school masking was associated with an additional 2882 Covid-19 cases among 46,530 staff (an estimated 81.7 cases per 1000 staff) and an additional 9168 Covid-19 cases among 294,084 students (an estimated 39.9 cases per 1000 students) during the 15 weeks. In school districts that had ended universal masking, approximately 40% of 7127 staff cases and 32% of 28,524 student cases were associated with the removal of universal masking policies.”