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After Campaign Led by UMD Researcher, WHO Changes Course

New Recommendations Acknowledge Possibility of Airborne Transmission

By Kelly Blake

People wearing masks in restaurant

Photo by Cheney Orr/Bloomberg via Getty Images

Employees and customers wear protective masks at a restaurant in Tucson, Arizona, in May. In an about-face, the World Health Organization today acknowledged the possibility COVID-19 could be transmitted through the air by breathing, following a letter to the organization from a UMD infectious disease expert and hundreds of colleagues urging the change.

A high-profile campaign led in part by a University of Maryland infectious disease expert moved the World Health Organization (WHO) today to acknowledge the novel coronavirus may remain airborne indoors and infect people through breathing.

The WHO backtracked on its previous position that only close contact and large droplets—which quickly fall to the ground—transmit the disease outside of medical settings following a July 6 letter directed to the medical community, WHO and Centers for Disease Control and Prevention from Dr. Don Milton, professor of environmental and occupational health in the UMD School of Public Health, and 239 scientific colleagues from 32 countries. 

They suggested the WHO’s messaging on that point was inadequate and based on outdated science. They urged recognition of the potential for airborne spread of COVID-19, and for global health authorities to do more to communicate this risk and advocate for the widespread use of preventive measures. Those include mask wearing when indoors in public spaces, avoiding crowds, improved ventilation and maintaining physical distance.

After intense scrutiny, the WHO today formally acknowledged “emerging evidence” that people can catch the virus from droplets floating in the air and that people may be at risk of becoming infected if they spend long periods in crowded indoor settings with poor ventilation.

However, Milton said the latest WHO recommendations are a mixed bag, and he expressed concern that they do not use a scientifically based definition of aerosols and therefore aren’t issuing strong enough mask-wearing recommendations.

“Recommending masks only within one meter is not supported by the science,” he said. “But, I am glad to see that even if they cannot admit that aerosol transmission is important, that they included the recommendations to ‘Avoid crowded places, close-contact settings and confined and enclosed spaces with poor ventilation’ and to ‘Ensure good ventilation in indoor settings, including homes and offices.’”

Scientifically sound control measures are needed to limit the severity of the pandemic and save lives in the U.S. and globally, particularly as decision-makers face tough choices around reopening schools and universities for the coming school year and people are returning to bars, restaurants, workplaces, churches, casinos and other indoor public spaces in places that have eased lockdowns, Milton said. 

“Viruses are released during exhalation, talking and coughing in microdroplets small enough to remain in the air and pose a risk of exposure to others who are further away than six feet,” said Milton, who runs the Public Health Aerobiology, Virology, and Exhaled Biomarker Laboratory. “Simple things can make a big difference in preventing spread of the coronavirus. Wear masks whenever you are not at home; even simple homemade masks can have a major impact. Open the windows. Don’t gather in large groups inside with singing or loud talking. These three simple things will save lives.”

Milton, who has shown that the infectious flu virus in microdroplets can be spread just by breathing and that masks can limit the amount of influenza virus in the exhaled air is now studying people how people spread SARS-CoV-2 to others and how to best prevent transmission. He and colleagues published data in April from a Hong Kong study showing that wearing surgical masks in public can reduce the amount of other coronaviruses in exhaled air and may help slow the COVID-19 pandemic's advance. This evidence was cited in a National Academies letter to the White House and was a major contributor to the United States government’s recommendation of face masks to prevent spread of the pandemic.

“You need to empower people with knowledge,” Milton said. “People can come up with creative ways to solve problems given the resources they have, but you are not empowering people to do what they can do by not telling them what the situation is.” 

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