Report on face masks’ effectiveness for Covid-19 divides scientists

A row has erupted among scientists over a new report into the use of face masks by the general public as an approach to managing the spread of Covid-19 in the community.

The report from a multidisciplinary group convened by the Royal Society called Delve – Data Evaluation and Learning for Viral Epidemics – has weighed up the evidence and come out in favour of the public wearing face masks, including homemade cloth coverings, in a bid to tackle Covid-19.

“Our analysis suggests that their use could reduce onward transmission by asymptomatic and pre-symptomatic wearers if widely used in situations where physical distancing is not possible or predictable, contrasting to the standard use of masks for the protection of wearers,” the report notes. “If correctly used on this basis, face masks, including homemade cloth masks, can contribute to reducing viral transmission.”Q&A

Coronavirus: should everyone be wearing face masks?

The conclusion is based on analysis of three key considerations, including the role of droplets as a route of transmission, and whether masks can help to reduce dispersal of droplets. However the authors note there are only a small number of studies.

But the report prompted other scientists to express their reservations, warning that it amounted to no more than opinion and overstated the available evidence.

Dr Simon Clarke, associate professor in cellular microbiology at the University of Reading, said the report “falls short of delivering new evidence and too casually dismisses precautionary principle when addressing the possibility that masks and coverings could have negative effects on people’s behaviours”.

He added: “Until more evidence is delivered in either direction, that’s all advice can be based on – opinions.”

Dr Ben Killingley, consultant in acute medicine and infectious diseases at University College London hospital, was also critical.

“The report is overly optimistic about the value of face coverings and it is incorrect to conclude that the evidence shows that face covering can reduce viral transmission in the community,” he said. “There is in fact no good evidence that face coverings achieve this.”

Killingley added that the report largely ignored real-world data, which suggests low effectiveness, albeit for protection of the wearer.

“This is not to say that face coverings might not be helpful,” he said, noting, face mask studies have not been carried out during a pandemic or in the context of a novel virus. “Nevertheless, the report, in my view, does not accurately represent the evidence on face coverings that currently exists,” he said.

Dr Antonio Lazzarino of the Department of Epidemiology and Public Health at University College London, agreed.

“That is not a piece or research. That is a non-systematic review of anecdotical and non-clinical studies,” he said.

“The evidence we need before we implement public interventions involving billions of people, must come ideally from randomised controlled trials at population level or at least from observational follow-up studies with comparison groups,” said Lazzarino noting that will allow experts to look at the pros and cons of wearing masks.

“Based on what we now know about the dynamics of transmission and the pathophysiology of Covid-19, the negative effects of wearing masks outweigh the positive,” he said.

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But Prof Trisha Greenhalgh, of the Nuffield Department of Primary Care Health Sciences at the University of Oxford, welcomed the report, saying it adds weight to the argument that face coverings by the general public could be part of a route out of lockdown.

“It draws together a wealth of evidence including the science of transmission and the efficacy of cloth-based materials both in laboratory studies and in randomised controlled trials, in relation to both source control and protection of the wearer,” she said.

“The authors flag the important finding that much if not most transmission of Sars-CoV-2 [coronavirus] happens from people who do not currently have symptoms. As would be expected from this distinguished group of scientists, the underlying evidence base is meticulously dissected and presented, including pointing out areas where more research is needed.”

Greenhalgh noted that while there have been concerns that use of masks by the public could reduce supply of medical-grade masks for healthcare workers, a homemade mask is sufficient for most people. “Medical-grade masks are not needed outside of healthcare settings. A cloth mask provides very good protection, and is more comfortable to wear,” she said.

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