(CNN)Stay 6 feet apart and, while you’re at it, wear a face covering.
The “most comprehensive study to date” found that physical distance and perhaps the use of a mask were the two best ways to prevent transmission of the new coronavirus.
The new study, published in the Lancet medical journal Monday, found people should stay at least three feet apart and more if possible.
The review of various published studies, paid for by the World Health Organization, had three main findings:
- Physical distancing: The chance of transmission at a distance of less than 1 meter (3.3 feet) was 12.8%, while that fell to 2.6% at a distance of more than 1 meter (3.3 feet). It added that distances of 2 meters (6.6 feet) could be more effective. It said that the certainty of the evidence was “moderate.”
- Face masks: The chance of transmission without a face mask or respirator (like an N95 mask) was 17.4%, while that fell to 3.1% when a mask was worn. However, the certainty of the evidence was “low.”
- Eye protection: The chance of transmission without eye protection was put at 16%, compared to 5.5% with some form of eye protection as a face shield, visor, goggles or glasses. However, the certainty of the evidence was “low.”
The researchers looked at 172 observational studies across 16 countries and six continents, including studies in health care and community settings. They didn’t look at randomized controlled trials, considered the gold standard but almost impossible to implement for studying transmission of infections in people.
The researchers at universities around the world analyzed studies from the outbreaks of Covid-19, severe acute respiratory syndrome virus of SARS and the Middle East respiratory syndrome virus (MERS), which are from the same family of viruses.
While most countries around the world have instituted simple steps like these to mitigate the spread of Covid-19, the scientific evidence behind them hasn’t always been clear-cut and has, in the case of masks, sometimes been contradictory.
All experts agree, however, on the importance of washing hands with soap thoroughly and regularly.
‘Major step forward’
The results of the review support a policy of physical distancing of at least 1 meter (3.3 feet) and, if feasible, 2 meters (6.6 feet) or more, the researchers said. The information could also be used to inform models that predict the spread of the disease and help with contact tracing schemes, the research team, led by Holger Schünemann of McMaster University in Canada, added.
Trish Greenhalgh, a professor of Primary Care Health Services at the University of Oxford who wasn’t involved in the research, said that while all these results were subject to uncertainty, the overwhelming message is that physical measures are effective in preventing Covid-19.
“This is a major step forward in our knowledge, since previous meta-analyses were mainly based on prevention of influenza and other diseases, which don’t behave the same way as the Covid-19 virus,” she told the Science Media Centre in London.
“In all three questions, the evidence appears to support the measures. For example, on average, staying 1 meter away from other people appears to reduce your chance of catching Covid-19 by 80%. Wearing a mask or face covering appears to reduce your risk by up to 85%. And wearing goggles or a face shield seems to reduce it by up to 78%.”
Current WHO guidance says that healthy people only need to wear a mask if they are caring for people with Covid-19. In the US, the Centers for Disease Control and Prevention recommends face coverings to protect others in places where social distancing can’t be maintained but says the general public does not need to wear surgical masks or masks with respirators.
Tarik Jašarević, a WHO spokesperson, said the international health agency was in the process of updating its advice on mask wearing, with a change likely to be announced this week.
The changes are “likely to touch on the best materials with which to make homemade masks, based on recent data from the US,” he told CNN via email.
“WHO has maintained a focus on mask use where there is evidence that they can limit transmission, such as in health care settings. In fact, the new guidance may expand their use in these settings,” he added.
Next steps for government leaders
The key question now was how should governments and the public interpret these results, said Linda Bauld, a professor of public health at the University of Edinburgh.
“The first and probably the most useful finding is that physical distancing matters. There have been plenty of complaints that the guidance in the UK on 2 meters distance is excessive because it is more than in other countries,” she told the Science Media Centre.
“But this review supports it. Maintaining this distance is likely to reduce risk compared to 1 meter. Thus where possible, this is the distance that retailers and employers should use as more premises and workplaces reopen in the future.”
Bauld added that while the certainty of evidence was low on face masks, making it more difficult for governments to make these mandatory, the review added to the evidence that leaders should be asking the public to wear face coverings on public transport, in stores and other indoor spaces even when physical distancing is in place, she said.
For health care workers, the study found that N95 masks and other respirator-type masks might give greater protection from viral transmission than surgical masks or multilayered cotton or gauze masks.
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The review did not, however, look at the effects of mask wearing for protecting other people, noted Oxford’s Greenhalgh. She said the general public should wear a cloth mask or standard surgical mask, leaving respirator masks for health care workers.
Even when properly used and combined, distancing, masks and eye protection do not offer complete protection, the study stressed, and basic measures like hand washing are essential to reduce transmission.