As COVID-19 ravaged the US in the first quarter of 2020, the US lacked a uniform mandatory policy for containing its spread. Governors facing enormous opposing pressures from businesses and medical professionals adopted various policies, especially lockdowns. The authors statistically analyze...

The effect of face masks on Covid-19 transmission is crucial for the health of populations. The effectiveness of face masks in reducing the transmission of Covid-19 varies across primary evidence. To perform a quantitative meta-analysis, we collected 258 estimates from 44 primary studies...