A rapid systematic review of the efficacy of face masks and respirators against coronaviruses and other respiratory transmissible viruses for the community, healthcare workers and sick patients.

This was a rapid review with a short search window and English-language papers only. Many positive findings came from subgroup or actual-use analyses after the main group comparisons were non-significant. Mask adherence was low in some community trials, and compliance was suboptimal in a source-control trial. Some healthcare worker trials lacked a control arm, so a non-significant difference between mask and respirator arms cannot prove equal protection. The Loeb healthcare worker trial used serologic outcomes and included vaccinated subjects despite claimed exclusion. This may have misclassified influenza cases. Several included trials were conducted by the review authors. Source-control trials were smaller, two had no clinical endpoints, and only three examined clinical outcomes in close contacts.

Do not conclude that medical masks protect healthcare workers as well as respirators. The two trials with no significant difference had no control arm, so they cannot separate equal protection from equal lack of protection.