The Impact of State Mask-Wearing Requirements on the Growth of Coronavirus Disease 2019 Cases, Hospitalizations, and Deaths in the United States.

In ecologic analyses of US states, piecewise multivariable models showed lower case-rate slopes after implementation of mask requirements: -1.0% (95% confidence interval, -1.34% to -.57%) and -0.44% (-.86% to -.03%) per 100 000 per day in early- and late-adopter states, respectively, compared with never-adopter states. Our findings support statewide mask requirements to mitigate transmission of coronavirus disease 2019.