Study provides evidence on optimal physical distancing, face masks, and eye protection to prevent spread of COVID-19

Keeping a minimum of one metre from other people as wearing face coverings and eye protection, in and outdoors of health-care settings, can be the most effective way to decrease the chance of viral infection or COVID-19 transmission, as stated by a systematic review and meta-analysis synthesizing all the available evidence from the scientific literature. It has been published in the Lancet.

However, none of those interventions, even when properly used and combined, ensure full protection from infection, and also the authors note that a number of the findings, particularly around face masks and eye protection, are supported by low-certainty evidence, with no completed randomized trials addressing COVID-19 for these interventions.

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The study, conducted to inform WHO guidance documents, is that the first time researchers have systematically investigated the optimum use of those protective measures in both community and healthcare settings for COVID-19. The authors say it’s immediate and important implications for curtailing the present COVID-19 pandemic and future waves by informing disease models, and standardizing the definition of who has been ‘potentially exposed’ for tracing contact.

Many countries and regions have issued conflicting advice about physical distancing to decrease COVID-19 transmission, supported by limited information. Additionally, the questions of whether masks and eye coverings might decrease COVID-19 transmission within the general population, and what the optimum use of masks in healthcare settings is, are debated throughout the pandemic.

“Our findings are the first to synthesise all direct information on COVID-19, SARS, and MERS, and provide the currently best available evidence on the optimum use of these common and simple interventions to help “flatten the curve” and inform pandemic response efforts in the community”, says Professor Holger Schünemann from McMaster University in Canada, who co-led the research. “Governments and the public health community can use our results to give clear advice for community settings and healthcare workers on these protective measures to reduce infection risk.”

The currently best available evidence suggests that COVID-19 is most ordinarily spread by respiratory droplets, especially when people cough and sneeze, entering through the eyes, nose, and mouth, either directly or by touching a contaminated surface. At the time, although there’s consensus that SARS-CoV-2 mainly spreads through large droplets and contacts, debate continues about the role of aerosol spreading.

For the present analysis, an international team of researchers did a review of 172 observational studies assessing distance measures, face masks, and eye protection to forestall transmission between patients with confirmed or probable COVID-19, SARS, or MERS infection and individuals near them (eg, caregivers, family, healthcare workers), till the 3rd of May, 2020.

Pooled estimates from 44 comparative studies involving 25,697 participants were included within the meta-analysis. Of these, 7 studies focused on COVID-19 (6,674 participants), 26 on SARS (15,928), and 11 on MERS (3,095).


The COVID-19 studies included within the analysis consistently reported a benefit for the three interventions and had similar findings to studies of SARS and MERS.

Analysis of knowledge from nine studies (across SARS, MERS and COVID-19, including 7,782 participants) observing physical distance and virus transmission found that keeping a distance of over one metre from others was related to a far lower risk of infection compared with but one metre (risk of infection when individuals stand quite a metre removed from the infected individual was 3% vs 13% if within a metre), however, the modelling suggests for each extra metre further away up to 3 metres, the chance of infection or transmission may halve. The authors note that the knowledge of their evidence on physical distancing is moderate, which none of the studies quantitatively evaluated whether distances of more than 2 metres were more effective, although meta-analyses provided estimates of risk.

Thirteen studies (across all three viruses, including 3,713 participants) that focus in eye protection found that face shields, goggles, and glasses were related to lower risk of infection, compared with no eye covering (risk of infection or transmission when wearing eye protection was 6% vs 16% when not wearing eye protection). The authors note that the certainty of the evidence for eye coverings is low.

Evidence from 10 studies (across all three viruses, including 2,647 participants) also found similar benefits for face masks generally (risk of infection or transmission when wearing a mask was 3% vs 17% when not wearing a mask). Evidence within the study was looking mainly at mask use within households and among contacts of cases, and was also supported on evidence of low certainty.

For healthcare workers, N95 and other respirator-type masks can be related to a greater protection from viral transmission than surgical masks or similar (eg, reusable 12-16 layer cotton or gauze masks). For the general public, face masks are probably related to protection, even in non-health-care settings, with either disposable surgical masks or reusable 12-16 layer cotton ones. However, the authors note that there are concerns that mass mask use risks diverting supplies from health-care workers and other caregivers at highest risk for infection.

They also stress that policy makers will need to quickly address access issues for face masks to ensure that they are equally available for all. “With respirators such as N95s, surgical masks, and eye protection in short supply, and desperately needed by healthcare workers on the front lines of treating COVID-19 patients, increasing and repurposing of manufacturing capacity is urgently needed to overcome global shortages”, says co-author Dr Derek Chu, Assistant Professor at McMaster University. “We also believe that solutions should be found for making face masks available to the general public. However, people must be clear that wearing a mask is not an alternative to physical distancing, eye protection or basic measures such as hand hygiene, but might add an extra layer of protection.”

The authors also stress the importance of using information about how acceptable, feasible, resource intense, and equally accessible to all the use of these interventions are when devising recommendations. “Across 24 studies of all three viruses including 50,566 individuals, most participants found these personal protection strategies acceptable, feasible, and reassuring, but noted harms and challenges including frequent discomfort and facial skin breakdown, increased difficulty communicating clearly, and perceived reduced empathy from care providers by those they were caring for”, says Dr Sally Yaacoub from the American University of Beruit in Lebanon.

According to co-author Karla Solo from McMaster University in Canada: “While our results provide moderate and low certainty evidence, this is the first study to synthesise all direct information from COVID-19 and, therefore, provides the currently best available evidence to inform optimum use of these common and simple interventions.”

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