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A preprint from the University of Edinburgh, uploaded to medRxiv*, has simulated the effect of facemasks on droplet spread.
Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:
“This adds to the growing evidence that under highly controlled laboratory conditions even simple face coverings can trap droplets produced during everyday activities such as talking or coughing, which in turn could lead to a reduction in the spread of any virus that might be carried on those droplets.
“However, the problem with these types of study is that they don’t go onto to look at the potential risk that virus-laden face coverings might pose when those coverings migrate from the confines of the lab and used in everyday life. To my mind any covering used by an infected individual has the potential to contaminate various surface if the wearer touches the covering – and let’s face it, it’s very difficult not to fiddle with them – and then goes on to touch something else without first cleaning their hands. So the message is clear, if you touch your mask then you need to clean your hands, otherwise if you are infected then you’re probably reducing their effectiveness at protecting others.”
Dr Julian Tang, Honorary Associate Professor in Respiratory Sciences, University of Leicester, said:
“Nice and timely study – which just confirms what we know mostly qualitatively with additional quantification of the degree to which ‘large’ droplets are contained by surgical and at least one type of home-made cloth mask.
“The authors could have expanded the range of masks tested, e.g. to address other recent questions, such as those around neck gaiters. It would have been useful to quantify the number of different sizes of smaller droplets (e.g. 1-30 micron diameter) penetrating through or around these masks, given the additional potential aerosol transmission risk – but this could be for a future follow-up study.
“However, I would be cautious about using these results alone to recommend a reduction in other measures like social distancing, as the degree to which aerosol transmission (not examined in this study) was not investigated – and there is actually no convincing evidence to support the statement that SARS-COV-2 COVID-19 is predominantly transmitted by large droplets, either.”
Prof Robert Dingwall, Professor of Sociology, Nottingham Trent University, said:
“The problems with this group’s research have been previously identified. Essentially, the use of a manikin to generate particles does not bear much resemblance to normal speaking and coughing. The photographs show that there is no attempt to replicate the thermal plume generated around the human body, which rises vertically and disrupts any expiration. The only air flow appears to have come from the manikin, which implies an artificial stilling of the air and elimination of other currents that would have contributed to the dispersal of the particles. Where human volunteers were used, particles were trapped at 5cm distance. It is well established by social science research in proxemics that only our closest and most intimate friends ever get that close under most circumstances.
“The translation of these findings to real world conditions is highly problematic. The most relevant statement in the press release is that the ‘new findings overestimate the protective effects of face coverings’.”
Prof Susan Michie, Director of UCL Centre for Behaviour Change, UCL, said:
“An important issue is what happens to those viral-laden masks when the virus is caught by them. If masks are disposed of or put into hot soapy water directly from the face without touching any part of the virus-contaminated parts of the mask, the block to transmission will be highly effective. But many mask wearers do not know or follow this advice so a more vigorous public information campaign is needed.”
Prof Paul Hunter, Professor in Medicine at the University of East Anglia, said:
“This is the latest in a number of papers showing this to be the case. Probably the best such paper so far was published some four months ago in Nature Medicine by Nancy Leung. https://www.nature.com/articles/s41591-020-0843-2
“In May, Amy Mueller and colleagues published another good paper looking at the effectiveness of cloth face coverings compared to surgical masks https://www.medrxiv.org/content/10.1101/2020.04.17.20069567v4. She found that face coverings could vary quite a lot in their effectiveness when compared to surgical masks.
“Even before the recent study by Bandiera, it was well accepted that in the laboratory setting masks can substantially reduce the number of droplets shed into the environment. The key issue remains how effective are such face masks in the real world when people may not wear them properly nor dispose of them correctly and may not continue to observe other social distancing requirements.”
* https://www.medrxiv.org/content/10.1101/2020.08.11.20145086v1
Declared interests
None received.