> Our main finding is that mask mandates and use likely did not affect COVID-19 case growth. Mask mandates were associated with greater mask use but ultimately

> Our main finding is that mask mandates and use likely did not affect COVID-19 case growth. Mask mandates were associated with greater mask use but ultimately did not influence total normalized cases or post-mandate case growth. > we did not observe lower growth rates over a range of compliance at maximum Fall-Winter growth [45-83% between South Dakota and Massachusetts during maxima] when growth rates were high. This complements a Danish RCT from 3 April to 2 June 2020, when growth rates were low, which found no association between mask use and lower COVID-19 rates either for all participants in the masked arm [47% strong compliance] or for strongly compliant participants only. > We only assessed one biological quantity [confirmed and probable COVID-19], but the ongoing pandemic warrants assessment of other factors such as hospitalizations and mortality. Importantly, our study does not disprove the efficacy of all masks in limited and controlled circumstances, such as properly worn N95 respirators. It's important to be aware that mandated non-pharmaceutical interventions like lock-downs, school closures, - and to a lesser degree masking - have second order effects on seasonal endemic illnesses such as influenza and RSV. Large future outbreaks of both diseases may occur following a period of extended NPIs. These outbreaks, which may reach peak numbers in the winter, could increase the burden to healthcare systems [1]. Considering these potential consequences, and the other potential negative externalities mentioned in the paper, it's imperative that such mandates be carefully scrutinized and evaluated before being widely enforced. [1] The impact of COVID-19 nonpharmaceutical interventions on the future dynamics of endemic infections https://www.pnas.org/content/117/48/30547 https://www.pnas.org/content/117/48/30547