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expert reaction to a study about facemask effectiveness

As study, published in Nature Medicine, reports on the effectiveness of facemasks.


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

“This new paper in Nature Medicine, while showing some interesting results, provides little new evidence to suggest that the existing WHO or UK government advice should be updated to advocate greater face mask wearing amongst the general public.

“The study shows that the majority of ill people who took part, despite breathing directly into a machine to detect viruses, did not have detectable levels of viruses in their breath, meaning that the virus is spread by coughs and sneezes. This might suggest that carriers who don’t have symptoms are less likely to spread virus than perhaps we’d assumed.  WHO guidance is already that people who are infected should wear masks. In the UK we go beyond that, by confining sick people to their homes. Your front door is better at preventing the spread of viruses than any mask.”


Prof Mark Harris, Professor of Virology, University of Leeds, said:

“This paper presents good evidence for use of facemasks to reduce transmission of respiratory viruses.  However, it is important to note the limitations of the study. 

“Firstly, the study only presents evidence that facemasks are effective in reducing shedding of virus from infected people, it does not address the issue of whether wearing a facemask can prevent infection of the wearer, which is the main reason that people wear facemasks in public spaces. The study measured shedding of virus in aerosols from patients with or without facemasks over a period of 30 minutes.  Even without a facemask only 4 out of 10 coronavirus infected patients shed any virus and the levels of virus released were up to 1 million times lower than in the nasal swabs. 

“Importantly the study only detected the presence of the virus genetic material and did not attempt to detect infectious virus.  In addition this study did not examine SARS-CoV-2 infected patients – instead the patients were infected with seasonal coronaviruses which do not cause the lower respiratory tract infection of SARS-CoV-2. Further studies focussing on SARS-CoV-2 are therefore warranted to confirm these observations.

“In my opinion the study presents important information about coronavirus transmission but, more importantly, again highlights the critical need for physical distancing and hand washing as the most effective ways of reducing spread of the virus.”


Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:

“This study backs up with compelling experimental evidence what WHO has been consistently saying from the outset of this outbreak. That surgical masks are an effective way for individuals who are infected to reduce the risk that they pose to others. It was interesting, albeit not too surprising, that their data showed this was true for a variety of viruses, for example the common cold, flu and coronaviruses, which are known or suspected to be carried on respiratory droplets.

“We need to remember though, that this stops short of providing evidence that wearing a mask reduces your risk of catching the virus from others. As a means of preventing infection to the wearer, this has previously only been shown useful in specific situations such as healthcare workers caring for sick patients, as these people have been properly trained in their use and also frequently change the mask.”


Dr Ben Killingley, an Infectious Diseases Physician, said:

“This paper adds more weight to WHO guidance that currently exists to support and encourage symptomatic individuals to wear a mask to reduce the dispersal of respiratory secretions. The findings here mirror those of a similar study conducted with individuals who had influenza.

“Important however that this should not been seen as an alternative to symptomatic individuals self isolating, the latter is far more likely to be effective if done well.”


Dr Rupert Beale, Group Leader, Cell Biology of Infection Laboratory, Francis Crick Institute, said:

“This new study presents strong and compelling evidence in favour of mask wearing as a means of reducing transmission of some viruses, including coronaviruses. Public health officials must immediately take note of this important new evidence. Mask wearing does not completely prevent transmission and it cannot be relied on as a sole measure, but combined with other social distancing measures mask wearing should form part of the ‘exit strategy’ from lockdown.”


*‘Respiratory virus shedding in exhaled breath and efficacy of face masks’ by Leung et al was published in Nature Medicine on Friday 3rd April.

We also sent out general comments on facemasks in response to journalist questions this morning:

All our previous output on this subject can be seen at this weblink:



Declared interests

None received.

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