Covid-19: Distancing, masks - what a comprehensive review says about their effectiveness

  • The first comprehensive review of all studies on Covid-19 protective measures
  • Masks and eye protection may help to a certain extent
  • No interventions guarantee protection without effective hand hygiene

The first comprehensive review of all available evidence for Covid-19 protective measures has been published in The Lancet.

The review takes a look at all published literature to inform the World Health Organization on the most effective safety measures.

All the studies reviewed looked at optimum use of protective measures in both community and healthcare settings, including physical distancing, eye protection and the wearing of face coverings such as masks, according to a news release.

The aim of this comprehensive release is to help establish definitive guidelines on protective measures, according to the statement.

Professor Holger Schünemann from McMaster University in Canada co-led this study and stated that it was the first to synthesise all direct information on Covid-19, SARS and MERS and provide the best available evidence in a response to the pandemic.

"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," he stated in a news release.

What are the overarching guidelines?

The current evidence indicates that Covid-19 is mostly spread by droplets from a cough or sneeze and that the SARS-Cov-2 virus enters the body by means of these drops via the eyes, nose and mouth, or by touching contaminated surfaces and then touching the face.

According to the news release, most of the evidence points to this method of transmission, while air transmission through finer droplets is still debated by experts.

The researchers looked at 172 studies, all addressing the current protective measures including physical distancing, wearing a mask and wearing an eye covering. These were the key findings from all the studies:

  • While physical distancing of 1m reduced the risk of infection, a distance of 2m is even more effective.
  • Studies that looked at face shields, goggles and protective glasses suggested that the risk is lowered, especially in health settings, but the evidence for the effectiveness of eye covering is low.
  • N95 and respirator-type masks remain the best measure of protection for healthcare workers, but for the general public, disposable surgical masks or cloth masks are adequate. Authors state that the public should refrain from using surgical and N95 masks, and that these should be reserved strictly for healthcare workers.
  • The authors emphasised that people must understand that wearing a mask does not mean that other measures of protection such as distancing and hand hygiene can fall away. The mask is simply an extra measure.
  • Most importantly, none of these interventions on their own offer complete protection without proper hand hygiene.

Study limitations must be taken into account

Although these findings are important for the guidance of health bodies such as the WHO, there are limitations. Few of the studies looked at the effect in non-healthcare settings and a lot of the evidence looked at SARS and MERS, not Covid-19.

There is also little evidence available on the exact effect of duration of exposure.

Review could spur on universal guidelines

However, Professor Raina MacIntyre (who was not involved in the study) from the Kirby Institute, University of New South Wales in Australia, states that this review is an "an important milestone", and writes, "For healthcare workers on Covid-19 wards, a respirator should be the minimum standard of care.”

She also stated that this review is important to help inform health authorities worldwide on the use of home-made masks and that there is currently no uniform design.

“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,” she said in the statement

Image credit: Anna Shvets from Pexels

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