June 1, 2020

expert reaction to review of optimal physical distancing, face masks, and eye protection to prevent spread of COVID-19

A study, published in The Lancet, looked at ptimal physical distancing, face masks, and eye protection to prevent spread of COVID-19.

Dr Simon Clarke, Associate Professor in Cellular Microbiology, University of Reading, said:

“This review of previously published research shows that many of the ways we’ve been advised to protect others and ourselves against Covid-19 have some evidence to support their usefulness. 

“However the authors note that the certainty of the evidence is low and other measures, like physical distancing, are by far the most effective at reducing spread of coronavirus.  It is pleasing to see that they call for robust randomised trials and proper risk assessments of control measures, rather than casual assumptions.

“Public Health messaging needs to be based on the best evidence available at the time that’s going to provide the most effective benefit for the most people and is easy to understand and follow. Simple messages like wash your hands and stay at home have been successful because they are easy to follow and they work.

“Where there is limited evidence for their effectiveness, the paper also notes that any protective coverings for eyes or face are only an extra layer of protection and suggestions that they are the answer to lifting lockdown restrictions misrepresent a robust review of evidence.  It remains the case that your front door is the most effective measure you have to protect yourself against Covid-19.”

Prof Linda Bauld, Professor of Public Health, University of Edinburgh, said:

“This is a useful and timely review on the available evidence to date regarding particular public health measures to prevent the spread of Covid-19. It adds to existing reviews, modelling and individual studies on the effectiveness of each of the main measures assessed (physical distancing, face masks and eye protection). The key question is: how should governments and the public interpret these results?

“The first and probably the most useful finding is that physical distancing matters. There have been plenty of complaints that the guidance in the UK on 2 meters distance is excessive because it is more than in other countries. But this review supports it. Maintaining this distance is likely to reduce risk compared to 1 meter.  Thus where possible, this is the distance that retailers and employers should use as more premises and workplaces reopen in the future. This is going to be very difficult in some settings but is important and we’ll all need to get used to maintaining this distance for some months to come.

“Leaving aside PPE in health and social care settings, on eye coverings and masks the certainty of the evidence is low. This makes it more difficult for governments to mandate these for the general public. But the review adds to the evidence that we should be asking the public to wear face coverings on public transport, in retail outlets and other indoor spaces even when physical distancing is in place. A combination of eye protection and masks (including face shields as we are observing in use in other countries) may be particularly important protection for some groups of employees as lock down eases.”

Prof Trish Greenhalgh FMedSci, Professor of Primary Care Health Services, University of Oxford, said:

“Meta-analysis is a mathematical way of combining the findings from more than one research study to get an average. It allows researchers to produce an overall estimate even when individual studies have different results or were too small to produce statistically significant findings. This paper reports meta-analysis of research on three questions: what is the effect of physical distancing; what is the effect of face masks; and what is the effect of eye coverings? All the studies looked specifically at the spread of SARS-CoV-2 (the virus that causes COVID-19) or one of two viruses from the same broad family (the ones that cause SARS and MERS).

“In all three questions, the evidence appears to support the measures. For example, on average, staying 1 metre away from other people appears to reduce your chance of catching COVID-19 by 80%. Wearing a mask or face covering appears to reduce your risk by up to 85%. And wearing goggles or a face shield seems to reduce it by up to 78%. Whilst all these results are subject to uncertainty, the overwhelming message is that physical measures are effective in preventing COVID-19. This is a major step forward in our knowledge, since previous meta-analyses were mainly based on prevention of influenza and other diseases which don’t behave the same way as the COVID-19 virus. 

“One caveat: whilst the study found that respirator masks, such as N95, were most effective at protecting the wearer, it did not look at the effect of mask-wearing for protecting other people.  As this study showed, respirator masks are irritant to the skin (they are designed to be worn for short periods then discarded), and other research has shown that most such masks are less effective at protecting other people than home-made cloth masks, because the respirator contains a one-way valve. For these reasons, a socially responsible citizen should be wearing (preferably) a cloth mask or else a standard surgical mask, NOT a respirator mask.”

‘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’ by Chu et al. was published in The Lancet at 23:30 UK time on Monday 1st June.

DOI: https://doi.org/10.1016/ S0140-6736(20)31142-9

Declared interests

None received