Face masks prevent transmission of respiratory diseases: a meta-analysis of randomized controlled trials
Coronavirus Disease 2019 (COVID-19) is caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and spreads through droplet-mediated transmission on contaminated surfaces and in air. Mounting scientific evidence from observational studies suggests that face masks for the general public may reduce the spread of infections. However, results from randomized control trials (RCT) have been presented as inconclusive, and concerns related to the safety and efficacy of non-surgical face
... non-surgical face masks in non-clinical settings remain. This controversy calls for a meta-analysis which considers non-compliance in RCTs, the time-lag in benefits of universal masking, and possible adverse effects. Methods: We performed a meta-analysis of RCTs of non-surgical face masks in preventing viral respiratory infections in non-hospital and non-household settings at cumulative and maximum follow-up as primary endpoints. The search for RCTs yielded five studies published before May 29th, 2020. We pooled estimates from the studies and performed random-effects meta-analysis and mixed-effects meta-regression across studies, accounting for covariates in compliance vs. non-compliance in treatment. Results: Face masks decreased infections across all studies at maximum follow-up (p=0.0318$, RR=0.608 [0.387 - 0.956]), and particularly in studies without non-compliance bias. We found significant between-study heterogeneity in studies with bias (I^2=71.2%, p=0.0077). We also used adjusted meta-regression to account for heterogeneity. The results support a significant protective effect of masking (p=0.0006, beta=0.0214, SE= 0.0062). No severe adverse effects were detected. Interpretation: The meta-analysis of existing randomized control studies found support for the efficacy of face masks among the general public. Our results show that face masks protect populations from infections and do not pose a significant risk to users. Recommendations and clear communication concerning the benefits of face masks should be provided to limit the number of COVID-19 and other respiratory infections.