The WHO also advised that widespread use of masks “carries uncertainties and critical risks”, such as self-contamination and shortages of medical supplies.
And it urged governments thinking of introducing the measure to give clear instructions to their citizens explaining the reasons as well as how, when and what to use.
It comes after Donald Trump said he would not wear a face mask despite a recommendation from the US Centers for Disease Control and Prevention that Americans wear cloth masks. President Trump went on to claim that scarves are better than non-medical masks.
Previous WHO guidance stated only people with coronavirus symptoms or looking after someone with suspected Covid-19 were advised to wear masks to cover their mouth and nose.
After appointing a group of experts to review the issue, the agency said on Monday there was limited evidence that wearing a medical mask by healthy individuals “may be beneficial as a preventive measure” if they are attending mass gatherings or are in contact with a sick patient.
“However, there is currently no evidence that wearing a mask (whether medical or other types) by healthy persons in the wider community setting, including universal community masking, can prevent them from infection with respiratory viruses, including Covid-19,” the agency added.
The WHO said the benefits of the wider use of masks included reducing the risk of exposure from infected patients before they display symptoms, and reducing the stigmatisation of infected people wearing masks.
However it advised governments of the following risks:
- self-contamination that can occur by touching and reusing contaminated mask
- potential breathing difficulties, depending on the type of mask use
- a false sense of security resulting in public reducing other public health measures such as regular hand-washing
- diversion of masks intended for health care workers, resulting in shortages
“Whatever approach is taken, it is important to develop a strong communication strategy to explain to the population the circumstances, criteria, and reasons for decisions,” the agency added.
Cotton cloth masks are “not considered appropriate” for health care workers after a study found they were at increased risk of infection compared to those who wore medical masks, the WHO added.
The WHO’s decision not to recommend the widespread wearing of masks was welcomed by William Keevil, professor of environmental healthcare at the University of Southampton.
“I believe the new WHO advice is the correct strategy,” he said. “There are many loose fitting surgical face masks on sale made of poor quality materials that wet easily from breath moisture and provide inadequate filtration.
“Even wearing Class 2 or 3 surgical face masks brings problems of fitting them correctly and ensuring their safe removal.”
Professor Keevil said that the untrained public tend to constantly touch and readjust the masks, contaminating their hands and risking contact with their eyes, a known route for virus entry. It is for this reason that healthcare professionals also use goggles or full-face visors.
He added: “The two-metre distancing rule should continue to be followed, as well as current self-isolation guidance, and needless to say: wash hands rigorously and frequently with soap and warm water, or failing that use an alcohol hand gel containing more than 60 per cent alcohol.”
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