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Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis

Our take —

To date, there is no evidence from randomized trials regarding the effect of wearing face masks on the risk of acquiring infection from SARS-CoV-2. In the absence of this urgently needed data, this systematic review and meta-analysis provides evidence, with a low degree of certainty, that wearing face masks may strongly reduce the risk of acquiring infection from cases. Moreover, there is evidence that N95 respirators, which are fitted to the user’s face, confer greater protection in health-care settings than other unfitted masks; no evidence was presented regarding differential effectiveness of respirators in community settings. This study does not address any potential reductions in transmission risk from mask-wearing on the part of an infectious person. Risk appears to be considerably reduced by maintaining a physical distance from infected individuals greater than 1 meter, with further risk reductions as the distance increases. However, these data come from non-randomized observational studies, only a small number of which were specific to SARS-CoV-2 (the majority came from studies of SARS and MERS).

Study design

Other

Study population and setting

This systematic review and meta-analysis included studies of SARS-CoV, MERS-CoV, and SARS-CoV-2 that assessed the effects of physical distancing, face masks, and eye protection on disease transmission. The review included 172 studies, 44 of which were comparative (including a total of 25,697 patients in health-care, household, and community settings) and were therefore used in pooled effect estimates in meta-analysis. Of these 44 studies, 7 were specific to SARS-CoV-2; pooled effect estimates were calculated separately for each coronavirus and combined into weighted averages across all studies. The authors used Cochrane and GRADE methods for the systematic review and assessment, and reported results using PRISMA and MOOSE guidelines. Risk of bias for each study was assessed via the Newcastle-Ottawa scale.

Summary of Main Findings

Across 10 adjusted studies and 29 unadjusted studies that included both health-care and non-health-care settings, wearing any type of face mask was associated with a lower risk of infection (unadjusted RR: 0.34, 95% CI: 0.26 to 0.45; adjusted OR: 0.15, 95% CI: 0.07 to 0.34). A stronger protective effect in health-care settings was observed with N95 respirators relative to other mask types (adjusted ORs of 0.04 vs. 0.33, p=0.09 for interaction). Wearing eye protection was associated with a lower risk of infection (unadjusted RR: 0.34, 95% CI: 0.22 to 0.52; adjusted RR: 0.25, 95% CI: 0.14 to 0.43). Physical distance of greater than 1 meter was associated with a lower risk of disease transmission relative to less than 1 meter (adjusted OR: 0.18, 95% CI: 0.09 to 0.38; risk difference: -10.2%, 95% CI: -11.5% to -7.5%). Increased distance was associated with lower viral transmission risk. The certainty of the results, according to the GRADE scale, was deemed to be moderate for distance and low for both face masks and eye protection. Risk of bias was deemed to be low-to-moderate. Across 24 studies examining attitudes and contextual factors regarding interventions, face mask use of multiple types was generally considered to be acceptable and feasible, despite reported challenges including discomfort.

Study Strengths

The systematic review was conducted according to established and transparent protocols. The meta-analyses used appropriate statistical techniques, and authors tested their results with well-described sensitivity analyses. Results were reported with a high degree of disaggregation and detail.

Limitations

The number of extant studies, particularly those specific to SARS-CoV-2, was small, and these studies were non-randomized. Mask use by an index case and its effect on transmissibility, on one hand, and mask use by contacts of the index case and its effect on susceptibility, on the other, are not distinguished as separate issues in either the analysis or the discussion. Mask types and usage were heterogeneous in the underlying studies, and the role of mask fit was not discussed, despite a potentially large impact on effectiveness. Measurement of interventions often relied on self-report and these data are subject to recall bias. Distance measurements in underlying studies were heterogeneous and imprecise. The duration of exposure was not assessed as a risk factor for transmission or as an effect modifier.

Value added

This review and meta-analysis provides the best available evidence for the possible protective effects of face masks, eye protection, and physical distancing on the risk of SARS-CoV-2 infection.

This review was posted on: 10 June 2020