Face coverings for the lay public: an alternative view

May 27, 2020

Trisha Greenhalgh

Several people have written to ask about the review on the Covid-19 Evidence website ‘Masks on or off’. In that review, Carl Heneghan and Tom Jefferson summarised the findings from a systematic review initially published in 2011 and updated this year. That review was mostly focused on medical masks for healthcare workers but also looked at randomised controlled trials of masks and face coverings for the lay public. Heneghan and Jefferson’s interpretation of that evidence was that there is insufficient evidence to support mask-wearing by members of the public. They also speculated that masks could cause harm.

My own interpretation of the evidence is different. I acknowledge that many scientists find the evidence unconvincing, and I fully agree with Carl and Tom that randomised controlled trial evidence of efficacy is lacking. Despite that, I believe that cloth face coverings (I prefer not to call them masks) for the public are an important public health measure in the current crisis, and I’m delighted that the UK government is now recommending cloth face coverings to be worn in confined public places.

Why are leading scientists so polarised on this issue?  It seems to me that we’re not disagreeing on what the evidence is, but what it means.  Here are some areas of contention:

  • Is the absence of a definitive randomised controlled trial, along with the hypothetical possibility of harm (for example from risk compensation) a good reason to hold back from changing policy? Some say yes; I say no.
  • Should we take account of stories reported in the lay press, such as those of single individuals apparently responsible for infecting dozens and even hundreds of others at rallies, prayer meetings or choir practices? Some say no; I say yes.
  • Should we extrapolate from laboratory experiments on the filtration capacity of different fabrics to estimate what is likely to happen when people wear them in real life? Some say no; I say yes.
  • Should we use anecdotal reports of some people wearing their masks “wrongly” or intermittently to justify not recommending them to everyone? Some say yes; I say no.
  • Should we take account of the possibility that promoting masks for the lay public may lead to a shortage of precious personal protective equipment (PPE) for healthcare workers? Some say yes; I say this is a supply chain issue which should not be confused with the scientific evidence of benefit.

I’ve written a peer-reviewed article defending my interpretation of the evidence, called ‘Face coverings for the lay public: laying straw men to rest’. You can read it here.

Disclaimer:  the article has not been peer-reviewed; it should not replace individual clinical judgement and the sources cited should be checked. The views expressed in this commentary represent the views of the authors and not necessarily those of the host institution, the NHS, the NIHR, or the Department of Health and Social Care. The views are not a substitute for professional medical advice.

Trish Greenhalgh is a Professor of Primary Care Health Sciences, co-Director of the Interdisciplinary Research In Health Sciences (IRIHS) unit, and joint module coordinator on the Knowledge Into Action (KIA) module of the MSc in Evidence Based Health Care.