An Analysis of Studies Pertaining to Masks in Morbidity and Mortality Weekly Report: Characteristics and Quality of Studies through 2023

This retrospective cross-sectional study assessed 77 studies on the effectiveness of masks published since 2019 in The Morbidity and Mortality Weekly Report (MMWR), a CDC publication. The authors found that 75% of these studies stated that masks are effective, but none of the studies were randomized, only 30% assessed effectiveness, and only 14.3% were statistically significant. Consequently, the authors concluded that the 'level of evidence generated was low and the conclusions were most often unsupported by the data.'