Evidence supports physical distancing, masks, and eye protection — WHO commissioned meta-analysis

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A comprehensive review of existing evidence supports physical distancing of two metres or more to prevent person-to-person transmission of COVID-19, says an international team led by McMaster University and St Joseph’s Healthcare Hamilton. Face masks and eye protection decrease the risk of infection, too.

The systematic review and meta-analysis was commissioned by the World Health Organisation. “Physical distancing likely results in a large reduction of COVID-19,” said lead author Holger Schünemann, professor of the departments of health research methods, evidence, and impact, and medicine at McMaster.

Schünemann is co-director of the WHO Collaborating Centre for Infectious Diseases, Research Methods and Recommendations. He also is director of Cochrane Canada and McMaster GRADE Centre.

“Although the direct evidence is limited, the use of masks in the community provides protection, and possibly N95 or similar respirators worn by health-care workers suggest greater protection than other face masks,” Schünemann said. “Availability and feasibility and other contextual factors will probably influence recommendations that organizations develop about their use. Eye protection may provide additional benefits.”

The systematic review was conducted by a large, international collaborative of researchers, front-line and specialist clinicians, epidemiologists, patients, public health and health policy experts of published and unpublished literature in any language.
They sought direct evidence on COVID-19 and indirect evidence on related coronaviruses causative of Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS). The team used Cochrane methods and the Grading of Recommendations, Assessment, and Evaluation (GRADE) approach which is used world-wide to assess the certainty of evidence.

They identified no randomised control trials addressing the three coronaviruses but 44 relevant comparative studies in health-care and non-health-care (community) settings across 16 countries and six continents from inception to early May 2020.

The authors noted more global, collaborative, well-conducted studies of different personal protective strategies are needed. For masks, large randomised trials are underway and are urgently needed.

The scientific lead is Derek Chu, a clinician scientist in the departments of health research methods, evidence, and impact, and medicine at McMaster and an affiliate of the Research Institute of St Joe’s Hamilton.

“There is an urgent need for all caregivers in health-care settings and non-health-care settings to have equitable access to these simple personal protective measures, which means scaling up production and consideration about re-purposing manufacturing,” said Chu.

“However, although distancing, face masks, and eye protection were each highly protective, none made individuals totally impervious from infection and so, basic measures such as hand hygiene are also essential to curtail the current COVID-19 pandemic and future waves.”

The work was funded by the World Health Organisation and involved close collaboration with the American University of Beirut, Lebanon and many international partners.

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes COVID-19 and is spread personto-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 (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 beta coronaviruses 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=25697 patients). Transmission of viruses was lower with physical distancing of 1 m or more, compared with a distance of less than 1 m (n=10736, 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; interaction=0·041; moderate certainty). Face mask use could result in a large reduction in risk of infection (n=2647; a OR 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 (reusable 12–16-layer cotton masks; p interaction=0·090; posterior probability >95%, low certainty). Eye protection also was associated with less infection (n=3713; a OR 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.

Derek K Chu, Elie A Akl, Stephanie Duda, Karla Solo, Sally Yaacoub, Holger J Schünemann, Derek K Chu, Elie A Akl, Amena El-harakeh, Antonio Bognanni, Tamara Lotfi, Mark Loeb, Anisa Hajizadeh, Anna Bak, Ariel Izcovich, Carlos A Cuello-Garcia, Chen Chen, David J Harris, Ewa Borowiack, Fatimah Chamseddine, Finn Schünemann, Gian Paolo Morgano, Giovanna E U Muti Schünemann, Guang Chen, Hong Zhao, Ignacio Neumann, Jeffrey Chan, Joanne Khabsa, Layal Hneiny, Leila Harrison, Maureen Smith, Nesrine Rizk, Paolo Giorgi Rossi, Pierre AbiHanna, Rayane El-khoury, Rosa Stalteri, Tejan Baldeh, Thomas Piggott, Yuan Zhang, Zahra Saad, Assem Khamis, Marge Reinap, Stephanie Duda, Karla Solo, Sally Yaacoub, Holger J Schünemann

McMaster University material


The Lancet abstract

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