Simple protective behavioural changes, namely physical distancing, face-mask use & eye protection, are associated with a significant risk reduction in coronavirus transmission.pearl
- Derek K Chu, Elie A Akl, Stephanie Duda, Karla Solo, Sally Yaacoub, Holger J Schünemann, and COVID-19 Systematic Urgent Review Group Effort (SURGE) study authors.
- Department of Health Research Methods, Evidence and Impact, McMaster University, Hamilton, ON, Canada; Department of Medicine, McMaster University, Hamilton, ON, Canada; The Research Institute of St Joe's Hamilton, Hamilton, ON, Canada.
- Lancet. 2020 Jun 27; 395 (10242): 1973-1987.
BackgroundSevere 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.MethodsWe 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.FindingsOur 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.InterpretationThe 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.FundingWorld Health Organization.© 2020 World Health Organization. Published by Elsevier Ltd. This is an Open Access article published under the CC BY 3.0 IGO license which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In any use of this article, there should be no suggestion that WHO endorses any specific organisation, products or services. The use of the WHO logo is not permitted. This notice should be preserved along with the article's original URL.
This article appears in the collections: Does face mask use reduce COVID transmission? and Anaesthesiology, Personal Protective Equipment (PPE) and COVID.
This important WHO-funded review and meta-analysis from Canada's COVID-19 SURGE group (Systematic Urgent Review Group Effort) looked at the effect of three non-pharmacological interventions on coronavirus transmission:
- Physical distancing
- Face masks
- Eye protection
Why is this important?
The speed of both the global spread of SARS-CoV-2 and national responses has lead to a bundled-approach to public health interventions for which the evidence-base is still catching up. This review provides reassurance that the core recommendations are likely beneficial.
What did they do?
Reflecting the lack of data, the review group analysed research covering not just SARS-CoV-2, but also SARS and MERS, capturing 172 observational studies with over 25,000 patients in both community and healthcare settings.
What did they find?
Perhaps unsurprisingly (though reassuring!) physical distancing > 1 meter was associated with lower transmission risk (risk difference 95% CI -11.5 to -7.5%) with increasing protection as distance increased beyond 2 meters.
Face-masks were also associated with reduced transmission (risk difference 95% CI -14.3% to -15.9%, though with low certainty), as was eye protection (risk difference 95% CI -12.5% to -7.7%).
N95 masks were even more strongly associated with risk reduction, as was mask use in a health-care setting vs non-health-care. Both N95 and multi-layer surgical masks were more protective than single-layer masks.
Simple protective behavioural changes, namely physical distancing, face-mask use and eye protection, are associated with a significant risk reduction in coronavirus transmission.
“...recognize, as an aspect of health worker safety, the precautionary principle that reasonable action to reduce risk, such as the use of a fitted N95 respirator, need not await scientific certainty”.
Campbell (2006) SARS Commission final report
Keep in mind...
Most of the 172 studies reported on bundled interventions (ie. PPE and distancing) so multi-factor analysis was required to tease out the individual contributions to risk reduction. Randomised trials are still pending...
The WHO changed it's advice regarding the general public wearing face-masks in response to the conclusions of this study.
The WHO now recommends the public wear face-masks when unable to physically distance.