Long after most nations urged their citizens to wear masks, and after months of hand-wringing about the quality of the evidence available, the World Health Organization on Friday endorsed the use of face masks by the public to reduce transmission of the coronavirus.
Since the beginning of the pandemic, surprisingly, the W.H.O. had refused to endorse masks. The announcement was long overdue, critics said, as masks are an easy and inexpensive preventive measure.
Even in its latest guidance, the W.H.O. made its reluctance abundantly clear, saying the usefulness of face masks is “not yet supported by high quality or direct scientific evidence,” but that governments should encourage mask wearing because of “a growing compendium of observational evidence.”
The W.H.O. also provided an exhaustive list of the potential disadvantages of wearing a mask, including “difficulty with communicating clearly” and “potential discomfort.”
A study funded by the W.H.O. concluded this week that respirator masks, like the N95, are better than surgical masks for health care workers. It also found that face shields, goggles and glasses may offer additional protection from the coronavirus.
But the W.H.O. did not budge from its previous recommendations for medical workers, saying that respirator masks are only needed if such workers are involved in procedures that generate virus-laden aerosols — droplets smaller than 5 microns.
Apart from those circumstances, transmission of the virus so far has only been demonstrated for larger droplets and by contact, said Dr. Benedetta Allegranzi, an infectious disease expert and technical lead for the W.H.O.
While studies have shown that viral R.N.A. is present in the air in certain health care settings, “transmission is different, and it has not been demonstrated,” she said.
“It is disappointing that the W.H.O. is dismissing that latest evidence that N95s are far more effective than surgical masks in protecting health care workers from Covid-19 exposure,” said David Michaels, an epidemiologist at George Washington University who headed the Occupational Safety and Health Administration during the Obama administration.
“If the problem is the shortage of N95s, the W.H.O. should acknowledge that and not pretend that medical masks are equally effective.”