Over the past six months, most of us have had to come to terms with a world previously known only to those living or working in the middle of an epidemic. And the fear of having our breath literally taken away prompted profound change.
Suddenly, it was best if we stayed apart; didn’t hug or shake hands; didn’t mass to work or eat or worship or roar for our favourite sports team. We masked, stepped back and stayed away. And wondered: but how far away?
Now, The Lancet has published the first review of all available evidence – including 172 observational studies – looking at how physical distancing, face masks and eye protection affect the spread of COVID-19, SARS and MERS in both community and healthcare settings across 16 countries.
The key findings are:
- that physical distancing of at least one metre lowers the risk of COVID-19 transmission, but two could be more effective
- that face coverings and masks might protect both healthcare workers and the general public against infection with COVID-19, and protective eye covering may also provide additional benefit – although the certainty of the evidence is low for both forms of protection
- and importantly, even when properly used and combined, none of these interventions offers complete protection and other basic protective measures – such as hand hygiene – are essential to reduce transmission.
The study – conducted to inform World Health Organisation guidance documents – is the first in which researchers have systematically examined the optimum use of these protective measures in both community and healthcare settings for COVID-19.
Around the world, there’s been conflicting advice about physical distancing to reduce transmission of COVID-19, based on limited information. The questions of whether masks and eye coverings might reduce transmission of in the general population, and what the optimum use of masks is in healthcare settings, have been debated during the pandemic.
“Our findings are the first to synthesise all direct information on COVID-19, SARS, and MERS, and provide the currently best available evidence on the optimum use of these common and simple interventions to help ‘flatten the curve’ and inform pandemic response efforts in the community,” says study co-leader Holger Schünemann, from McMaster University, Canada.
“Governments and the public health community can use our results to give clear advice for community settings and healthcare workers on these protective measures to reduce infection risk.”
The currently best available evidence suggests that COVID-19 is most commonly spread by respiratory droplets, especially when people cough and sneeze, entering through the eyes, nose and mouth, either directly or by touching a contaminated surface.
In spite of this consensus that SARS-CoV-2 mainly spreads through large droplets and contact, debate continues about the role of aerosol spreading.
The COVID-19 studies included in the analysis consistently reported a benefit for the three interventions and had similar findings to studies of SARS and MERS.
The authors stressed the importance of taking into account the acceptability, feasibility and accessibility of these interventions when devising their recommendations.
“Across 24 studies of all three viruses including 50,566 individuals, most participants found these personal protection strategies acceptable, feasible and reassuring,” says co-author Sally Yaacoub, from the American University of Beruit, Lebanon.
“While our results provide moderate- and low-certainty evidence, this is the first study to synthesise all direct information from COVID-19 and, therefore, provides the currently best available evidence to inform optimum use of these common and simple interventions,” says co-author Karla Solo, also from McMaster University.
While the review’s findings are important, its limitations include that few studies assessed the effect of interventions in non-healthcare settings, and most evidence came from studies of SARS and MERS. Finally, the effect of the duration of exposure on risk for transmission was not specifically examined.
In a linked commentary, Raina MacIntyre from the University of New South Wales, Australia, and Quanyi Wang, from the Beijing Centre for Disease Prevention and Control, China, who were not involved with the study, describe it as “an important milestone”.
“For health-care workers on COVID-19 wards, a respirator should be the minimum standard of care,” they write.
“This study… should prompt a review of all guidelines that recommend a medical mask for health workers caring for COVID-19 patients. Although medical masks do protect, the occupational health and safety of health workers should be the highest priority and the precautionary principle applied.”
The commentary continues: “[The authors] also report that respirators and multilayer masks are more protective than are single layer masks. This finding is vital to inform the proliferation of home-made cloth mask designs, many of which are single-layered.
“A well designed cloth mask should have water-resistant fabric, multiple layers, and good facial fit… Universal face mask use might enable safe lifting of restrictions in communities seeking to resume normal activities and could protect people in crowded public settings and within households.”
Ian Connellan is the editor of Cosmos magazine.
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