April 6, 2020

expert reaction to a preprint about facemask effectiveness

A preprint, posted on MedRxiv, reports on the effectiveness of facemasks.

Dr Michael Head, Senior Research Fellow in Global Health, University of Southampton, said:

“This new review of the literature is very timely, and focuses on the wearing of face masks, a topic that has been widely discussed during this pandemic. The review shows that face masks are potentially useful in specific circumstances, for example in relation to movements around vulnerable patients such as those in hospital with weaker immune systems. There was also evidence of a potential small protective effect when facemasks were worn in community settings where the contact was quite brief e.g. in shops.

“However, these protective effects appear to be very small, and the studies reviewed typically contained significant biases (for example, when reporting user compliance). Thus, despite this excellent review, there are still uncertainties around future policies that consider face masks. The authors conclude that the evidence does not currently support the widespread and routine use of facemasks in the community.”

Dr Jennifer Cole, Biological Anthropologist, Royal Holloway, University of London, said:

“It is important to stress that this study concludes: ‘We do not consider that the balance of evidence across all available studies supports routine and widespread use of facemasks in the community’. This study therefore supports the importance of prioritising limited stocks for healthcare staff and other key workers in the high-risk settings identified by the study as more likely to benefit from mask use. It is important to synthesize what we know right now, and even though these studies largely do not relate to the current outbreak, it is the best knowledge available at present.

“The paper does not differentiate between people who chose voluntarily to wear facemasks and those for whom wearing facemasks was made compulsory, however. To fully understand the impact of mask wearing, it is essential to relate it to other behaviours – for instance, are those people who choose to be ‘early adopters’ of mask wearing also more careful about disease transmission in general, and so more likely to observe appropriate social distancing and regular hand washing – which would confound the results of the value they gain from the mask – and equally are those who are told to wear it less likely to take notice of other mitigations, such as regular hand-washing and social distancing because they see the mask as offering a security that it may not, in fact, deliver.

“There is understandably a lot of concern over face masks at the moment but it is extremely important that the supplies that are available are prioritised for healthcare workers and for other frontline essential workers such as supermarket checkout staff and public transport operators who are having multiple physical interactions with the public each day. While the study concludes that more research is needed before we have conclusive evidence it is extremely important that a key takeaway is that ‘We do not consider that the balance of evidence across all available studies supports routine and widespread use of facemasks in the community’. This must not be sidelined in favour of more sensationalist headlines.”

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

“This research, while not yet peer-reviewed by scientists, is a reasonable review of previous studies and presents the existing evidence fairly – which is that there is only very limited evidence of the benefits of wearing face masks by the general public, no evidence that wearing them in crowded places helps at all, and no evidence at all yet related to Covid-19.  It’s noteworthy that it aligns with the findings of a similar review of research studies by the World Health Organization, published in October of last year, which concluded that there was no evidence that face masks are effective in reducing transmission of flu.

“The authors also acknowledge that mass face mask-wearing by the public would likely cause shortages among people who genuinely need protective equipment – health care workers on the frontline in our hospitals.”

Prof Mike Barer, Professor of Microbiology, University of Leicester, said:

“At a first reading this is a valuable review of observations made on the effectiveness masks or facial coverings worn in public in preventing symptomatic viral or virus-like respiratory illnesses . The authors have gathered a systematic body of evidence that others may use to arrive at their own conclusions.

“The maximum effect detected was a reduction in the risk of infection by 20%, i.e. of 5 exposed individuals who get infected, it was estimated that only 4 would have been infected if masks had been used; in most cases the effect was substantially less than this. It is important to appreciate that the review does not address the value of masks in healthcare and other high risk situations.”

‘Facemasks and similar barriers to prevent respiratory illness such as COVID-19: A rapid systematic review’ by Brainard et al was published on the preprint server medRxiv on 6th April 2020. This work has not been peer-reviewed.

https://www.medrxiv.org/content/10.1101/2020.04.01.20049528v1

All our previous output on this subject can be seen at this weblink: www.sciencemediacentre.org/tag/covid-19

Declared interests

None received.