Before 2020, evidence for the efficacy of community masking – that is, asking ordinary members of the public to wear cloth or surgical masks when going about their business – was shaky at best.
This evidence was reviewed in detail by Jeffrey Anderson, a former director of the Bureau of Justice Statistics. He notes that:
of the 14 RCTs that have tested the effectiveness of masks in preventing the transmission of respiratory viruses, three suggest, but do not provide any statistically significant evidence in intention-to-treat analysis, that masks might be useful. The other eleven suggest that masks are either useless—whether compared with no masks or because they appear not to add to good hand hygiene alone—or actually counterproductive.
In another piece that’s well worth reading, Professor Steve Templeton provides a list of quotations from what he calls “the BP era” (Before Things Got Political). Each quotation, taken from one or other expert, testifies to the lack of evidence that community masking works against respiratory pathogens.
For example, in a systematic review published early last year, Jingyi Xiao and colleagues “did not find evidence that surgical-type face masks are effective in reducing laboratory-confirmed influenza transmission, either when worn by infected persons… or by persons in the general community to reduce their susceptibility”.