Face masks to prevent transmission of respiratory infections: Systematic review and meta-analysis of randomized controlled trials on face mask use

Abstract

Objectives To examine the use of face mask intervention in mitigating the risk of spreading respiratory infections and whether the effect of face mask intervention differs in different exposure settings and age groups. Design Systematic review and meta-analysis. We evaluated the risk of bias using the Cochrane Risk of Bias 2 tool (ROB2). Data sources We searched PubMed, Embase, Cochrane Central Register of Controlled Trials, and Web of Science were searched for randomized controlled trials investigating the effect of face masks on respiratory infections published between 1981 and February 9, 2022. We followed the PRISMA 2020 guidelines. Eligibility criteria for selecting studies We included randomized controlled trials investigating the use of face mask intervention in mitigating the risk of spreading respiratory infections across different exposure settings. Results We identified 2,400 articles for screening. 18 articles passed the inclusion criteria for both evidence synthesis and meta-analysis. There were N = 189,145 individuals in the face mask intervention arm and N = 173,536 in the control arm, and the follow-up times ranged from 4 days to 19 months. Our results showed between-study heterogeneity (p < 0.0001). While there was no statistically significant association over all studies when the covariate unadjusted intervention effect estimates were used (RR = 0.977 [0.858–1.113], p = 0.728), our subgroup analyses revealed that a face mask intervention reduced respiratory infections in the adult subgroup (RR = 0.8795 [0.7861–0.9839], p = 0.0249) and in a community setting (RR = 0.890 [0.812–0.975], p = 0.0125). Furthermore, our leave-one-out analysis found that one study biased the results towards a null effect. Consequently, when using covariate adjusted odds ratio estimates to have a more precise effect estimates of the intervention effect to account for differences at the baseline, the results showed that a face mask intervention did reduce respiratory infections when the biasing study was excluded from the analysis (OR = 0.8892 [0.8061–0.9810], p = 0.0192). Conclusion Our findings support the use of face masks particularly in a community setting and for adults. We also observed substantial between-study heterogeneity and varying adherence to protocol. Notably, many studies were subject to contamination bias thus affecting the efficacy of the intervention, that is when also some controls used masks or when the intervention group did not comply with mask use leading to a downward biased effect of treatment receipt and efficacy. Trial registration PROSPERO registration number CRD42020205523.

Unmasking the truth: Experimental evidence of facemask compliance in Bangladesh, Kenya, and Nigeria during the COVID-19 pandemic

“…Although smaller in the other countries, the gap was still almost 30 percentage points in Nigeria and 20 percentage points in Bangladesh. In Bangladesh, experimentally induced differences in facemask compliance of approximately 30 percentage points were associated with a reduction in symptomatic seroprevalence of COVID-19 by over 11% [ 5 ]. Other studies have also generally found that high levels of compliance are needed to reduce transmission at the community level [ 4 , 31 , 32 ].…”

“…This may be especially true in LMIC settings where resources to enforce mandates may be more limited. A recent large scale randomized trial implemented in Bangladesh to test strategies to increase mask usage found that the free provision alone of masks had only a small effect on uptake but that periodic monitoring in public places led to large increases in mask-wearing and that these effects were sustained over long periods [ 5 ]. The monitoring intervention also led to increases in other preventive behaviors, namely physical distancing, which further points to the importance of social norms and pro-social learning in the promotion of public health measures.…”

“…A randomized trial conducted in Bangladesh has confirmed that facemasks can reduce the number of symptomatic COVID-19 cases at the population [ 4 ]. More recently, a systematic review of randomized trials also found that facemasks were effective at reducing the incidence of all forms of respiratory illness in community settings, and among adults, although the unadjusted results across all the studies identified in the review were not statistically significant [ 5 ]. As facemask wearing is relatively harmless, some have also argued that it should be adopted based on the precautionary principle [ 6 ].…”

“…In this paper, we use a list experiment to estimate actual compliance with facemask mandates among people living in three LMICs during the COVID-19 pandemic. At the time of our survey, all three countries had mandatory facemask policies in place: in Kenya, the Ministry of Health mandated masks in public places starting in early April 2020 [ 24 ], the Nigerian President mandated everyone to wear a mask in public starting in late April 2020, although similar policies had already been adopted in most states before this policy change [ 25 ], and in late May a similar policy had been put into place in Bangladesh [ 5 ].…”

The effect of activity and face masks on exhaled particles in children

“…[34][35][36] Nonetheless, the evidence supporting the use of face masks in children is almost primarily based on studies of adults. [37][38][39] and there remains a lack of consensus around the effectiveness of face masks in preventing pediatric respiratory viral transmission. [40][41][42] Following evolving guidance from the Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics, most schools have relaxed masking recommendations in communities where COVID-19 transmission rates and hospital admission rates are low and hospitals have sufficient capacity.…”