Anyone Living in Areas With ‘Widespread’ COVID-19 Transmission Should Wear Masks, WHO Says

Months after many cities and countries directed their residents to wear fabric face masks to prevent the spread of COVID-19 even if they are healthy, the World Health Organization (WHO) has issued the same guidance for the global community.

At a press briefing on June 5, WHO Director-General Dr. Tedros Adhanom Ghebreyesus announced that the organization now recommends people who live in areas experiencing “widespread transmission” of COVID-19 wear a fabric mask whenever social distancing of at least one meter (about three feet) is not possible. The guidance applies even to those not showing symptoms of coronavirus, as research now strongly suggests many people with the disease are asymptomatic or only mildly symptomatic. People in high-risk groups, including the elderly and those with underlying conditions, should try to wear a medical-grade mask.

“Governments should encourage the general public to wear masks where there is widespread transmission and physical distancing is difficult, such as on public transport or in shops,” Ghebreyesus said.

The WHO’s guidance also describes the most effective materials to use in a fabric face mask. Ideally, masks should consist of three layers: an inner layer made of an absorbent material like cotton, which can trap the wearer’s own respiratory droplets; a middle layer made of a non-woven material, like polypropylene, that acts as a filter; and an outer layer made of a non-absorbent material like polyester, which stops outside particles from getting in.

If that’s not possible, the WHO recommends at least folding or sewing your mask such that it has multiple layers. Stretchy, elastic fabrics aren’t ideal because they don’t filter very well, and can’t be washed in hot water. (Fabric masks should be washed frequently with hot water and soap or detergent, the WHO says.)

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Previously, the WHO only advised individuals experiencing symptoms or caring for people sick with coronavirus to wear masks, although many areas have already implemented more expansive policies at the local level. The U.S. Centers for Disease Control and Prevention (CDC) first recommended the widespread use of fabric face coverings on April 3, for example.

The WHO’s delay illustrates the difficulty of drafting and communicating public-health guidance for the entire world, even in a fast-moving pandemic. “Every recommendation that we put out needs to be applicable for every type of situation. That’s a blessing and a curse,” Dr. Maria Van Kerkhove, the WHO’s technical lead on COVID-19, told TIME. “We need to put out guidance that’s appropriate for all, but it means we cannot be as specific for every exact situation.”

Masks have been a particularly contentious topic during the COVID-19 pandemic. At first, most health officials strongly dissuaded the general public from wearing masks—in large part because of supply issues, but also because some researchers said there was not enough evidence to support the practice. But as more research emerged about asymptomatic transmission—suggesting that even seemingly healthy people could be spreading the virus—and the efficacy of face masks, most health groups reversed course.

Still, there’s gray area even in the WHO’s latest guidance. For instance, it recommends masks for healthy people only in areas with widespread coronavirus transmission—but what does that mean, exactly?

Van Kerkhove says the guidance applies to areas with intense community spread (demonstrated by lots of people getting sick without a clear point of exposure) and an inability to isolate, test and contact trace everybody who becomes infected. But interpreting that criteria is largely up to individual officials, since the WHO cannot know the intricacies of each local environment, Van Kerkhove says. “It needs to be done at the lowest administrative level as possible to make this work,” she says.

That’s a necessary reality, perhaps, but one that renders international policies more guidelines than rules.

The WHO has also upgraded its guidance for health care workers. The group has directed health care professionals treating confirmed or suspected COVID-19 patients to wear face masks (as well as other personal protective equipment) since the beginning of the outbreak. Now, all physicians who are treating patients of any kind in high-transmission areas should wear medical-grade masks for their entire shifts, the WHO says. The new policy is meant to help eliminate asymptomatic or mild transmission in health care environments.

Even with the new guidelines, Van Kerkhove emphasizes that “masks alone are not enough.”

“Anyone who is unwell should be at home. All suspect [cases] should be tested. Confirmed cases should be isolated and cared for. Contacts should be quarantined,” she says. “If that were actually taking place, we would drastically, drastically reduce transmission. We’re trying to put into context the use of an additional tool, a fabric mask, that can be used in certain situations.”