Effectiveness of cloth face masks to prevent viral spread: a meta-analysis

Background The effectiveness of cloth face masks to prevent viral spread has not yet been conclusively established. In this meta-analysis, we evaluate their effectiveness in comparison to standard medical/surgical and N95-typed masks against viral spread.Methods We identified literature through a systematic search in three databases and meta-analytically synthesized relevant studies by means of random-effects as well as multilevel modelling.Results Twelve studies comprising k = 28 effect sizes (N = 338) were included. Medical/surgical and N95-typed masks outperformed cloth masks, yielding a large effect (g = 1.40). This effect remained robust when data were grouped according to comparisons with medical/surgical masks (g = 1.25) and N95-typed masks (g = 1.29). However, effects were differentiated according to mask fit, indicating reversals of signs when cloth mask effects were compared with ill-fitting medical/surgical and N95-typed masks (gs = -12.50 and - 10.90, respectively).Conclusions Cloth face masks were found to have significantly poorer filtering performance than medical/surgical masks and N95 masks, but only if non-cloth masks were properly fitted. Our results illustrate the necessity of using well-fitting medical/surgical or N95-typed masks to prevent viral spread, although some allowance should be made in circumstances where higher compliance with cloth mask mandates are expected.