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Chu DK, Akl EA, Duda S, et al. 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. Lancet. 2020 Jun 27;395(10242):1973-1987. doi: 10.1016/S0140-6736(20)31142-9. Epub 2020 Jun 1. (Systematic review)

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes COVID-19 and is spread person-to-person through close contact. We aimed to investigate the effects of physical distance, face masks, and eye protection on virus transmission in health-care and non-health-care (eg, community) settings.

METHODS: We did a systematic review and meta-analysis to investigate the optimum distance for avoiding person-to-person virus transmission and to assess the use of face masks and eye protection to prevent transmission of viruses. We obtained data for SARS-CoV-2 and the betacoronaviruses that cause severe acute respiratory syndrome, and Middle East respiratory syndrome from 21 standard WHO-specific and COVID-19-specific sources. We searched these data sources from database inception to May 3, 2020, with no restriction by language, for comparative studies and for contextual factors of acceptability, feasibility, resource use, and equity. We screened records, extracted data, and assessed risk of bias in duplicate. We did frequentist and Bayesian meta-analyses and random-effects meta-regressions. We rated the certainty of evidence according to Cochrane methods and the GRADE approach. This study is registered with PROSPERO, CRD42020177047.

FINDINGS: Our search identified 172 observational studies across 16 countries and six continents, with no randomised controlled trials and 44 relevant comparative studies in health-care and non-health-care settings (n=25 697 patients). Transmission of viruses was lower with physical distancing of 1 m or more, compared with a distance of less than 1 m (n=10 736, pooled adjusted odds ratio [aOR] 0·18, 95% CI 0·09 to 0·38; risk difference [RD] -10·2%, 95% CI -11·5 to -7·5; moderate certainty); protection was increased as distance was lengthened (change in relative risk [RR] 2·02 per m; pinteraction=0·041; moderate certainty). Face mask use could result in a large reduction in risk of infection (n=2647; aOR 0·15, 95% CI 0·07 to 0·34, RD -14·3%, -15·9 to -10·7; low certainty), with stronger associations with N95 or similar respirators compared with disposable surgical masks or similar (eg, reusable 12-16-layer cotton masks; pinteraction=0·090; posterior probability >95%, low certainty). Eye protection also was associated with less infection (n=3713; aOR 0·22, 95% CI 0·12 to 0·39, RD -10·6%, 95% CI -12·5 to -7·7; low certainty). Unadjusted studies and subgroup and sensitivity analyses showed similar findings.

INTERPRETATION: The findings of this systematic review and meta-analysis support physical distancing of 1 m or more and provide quantitative estimates for models and contact tracing to inform policy. Optimum use of face masks, respirators, and eye protection in public and health-care settings should be informed by these findings and contextual factors. Robust randomised trials are needed to better inform the evidence for these interventions, but this systematic appraisal of currently best available evidence might inform interim guidance.

FUNDING: World Health Organization.

Discipline Area Score
Respirology/Pulmonology 7 / 7
Infectious Disease 6 / 7
Public Health 6 / 7
Occupational and Environmental Health 6 / 7
Family Medicine (FM)/General Practice (GP) 6 / 7
General Internal Medicine-Primary Care(US) 6 / 7
Hospital Doctor/Hospitalists 6 / 7
Internal Medicine 6 / 7
Emergency Medicine 6 / 7
Intensivist/Critical Care 6 / 7
Comments from MORE raters

Emergency Medicine rater

Rigorous synopsis.

Emergency Medicine rater

As an ED doc, I work in fairly close proximity with others, so I am happy to see 1 meter may be enough, although 2 is better. I wear an N95 the entire shift, so happy to see that it is decent protection, but it's interesting to see that perhaps I should wear one out in public as well. This is altogether a useful review of the poor evidence out there.

Family Medicine (FM)/General Practice (GP) rater

A well-constructed systematic review that has led to some revisions around policy, including recent CDC guideline updates advocating for eye protection in settings with increased COVID-19 exposure.

General Internal Medicine-Primary Care(US) rater

I think this is important since we are having so many protests with non-mask wearers, inefficient mask wearers, and homemade mask wearers, and, of course, no-mask wearers as they don't believe it is important

Hospital Doctor/Hospitalists rater

As with any other virus, measures to prevent transmission such as face masks and "social distancing" have been assumed to be effective. Although this meta-analysis was large in scale, it included no RCTs and many of the studies included had high risk for bias.

Infectious Disease rater

This is an excellent summary that reinforces and helps to quantify the evidence concerning methods to reduce coronavirus transmission.

Intensivist/Critical Care rater

This is for carefull reading as it contains only non-experimental studies and most are non-COVID-19 related.

Internal Medicine rater

Obviously, this is highly topical and affects all clinical interactions. My only worry is that this field moves so quickly that almost everything is out of date by the time it gets disseminated.

Occupational and Environmental Health rater

Very concerned about combining studies from three different viral pathogens and extrapolating to COVID-19. The pathogenicity of each of these viruses is quite different, so combining may give skewed results.

Public Health rater

This is a complicated issue with incomplete information and lots of variability as to how masks are used by folks. Considering the Covid-19 pandemic, this is still useful and relevant information.

Public Health rater

Impressive methods that assessed the 'best evidence' currently available to reinforce infection control procedures.

Respirology/Pulmonology rater

This meta-analysis affirms current recommendations regarding the effectiveness of physical distancing and respiratory and eye protection. It will be very useful for informing and developing public policy for disease mitigation.

Respirology/Pulmonology rater

This is important, timely, and relevant scientific information with significant public health implications. Rapid dissemination is essential to help individuals and the health care community make informed choices to manage their risk for coronavirus infection. Please disseminate quickly.
Comments from EvidenceAlerts subscribers

Mrs. Silke Richter (11/2/2020 5:10 AM)

Unfortunately, the appraisal of the studies in this review that examine the benefit of face masks in community settings does not properly take into account their limitations. Risk of bias in the included studies could have altered the results and meta-analysing the three very heterogeneous studies is highly questionable. The effect estimate is in sharp contrast to other systematic reviews.

Dr. mohammad almutawa (7/2/2020 12:13 PM)

Well done metanalysis that is timely and relevant. It is important to note that "community settings" are a general term. Caution should be used when extrapolating results to schools, particularly younger students, since it doesn't examine the potential of increased touching of the face in this group where mask use may be a risk factor.