The introduction of a mandatory mask policy was associated with significantly reduced COVID-19 cases in a major metropolitan city
PLoS ONE (2021) - Comments
doi: 10.1371/journal.pone.0253510  issn: 1932-6203  pubmed: 34288910 

Nick Scott, Allan Saul, Tim Spelman, Mark Stoove, Alisa Pedrana, Alexander Saeri, Emily Grundy, Liam Smith, Michael Toole, Chandini Raina McIntyre, Brendan S. Crabb, Margaret Hellard