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WHO plans to address airborne COVID-19 transmission


The World Health Organization is preparing a scientific brief to address the continually emerging evidence on transmission of COVID-19 and plans to release its guidance “in the coming days.”

WHO will likely address airborne transmission of the virus after a commentary from almost 240 multidisciplinary scientists raised the alarm that virus particles could remain airborne longer that previously appreciated, particularly in poorly ventilated indoor spaces.

“Airborne route of infection transmission is significant, but so far completely undermined, and not recognized by the decision makers and bodies responsible for infection control,” lead commentary author Lidia Morawska, PhD, told Medscape Medical News.

“This means that no control measures are taken to mitigate airborne transmission and, as a consequence, people are infected and can die,” said Morawska, director of the International Laboratory for Air Quality and Health at Queensland University of Technology in Brisbane, Australia. “We wanted to bring this to the attention of the world to prevent this from happening.”

The commentary was published July 6 in Clinical Infectious Diseases.

WHO leaders defended their progress in announcing any changes regarding how COVID-19 can be transmitted during a virtual press briefing today. They have collaborated since April with some of the scientists who coauthored the commentary, for example, said Maria Van Kerkhove, PhD, WHO technical lead on COVID-19.

“We have been working on a scientific brief ... to consolidate knowledge around transmission,” she added.

One focus will be on how masks protect healthcare workers. “We are also looking at the possible role of airborne transmission in other settings,” Van Kerkhove said. “We will be releasing our brief in the coming days.”

“We acknowledge there is emerging evidence in this field,” Benedetta Allegranzi, MD, WHO technical lead on COVID-19, said during the briefing from Geneva. “Therefore, we believe we have to be open to this evidence and its implications.”

WHO participated in an international research meeting last week that addressed means for controlling modes of COVID-19 transmission, Allegranzi said. “Our group and others really highlighted importance of research on different modes of transmission, including droplets of different sizes and their relative importance,” she said. Another aim was determining the dose of the virus required for airborne transmission.

“These fields of research are really growing but not definitive. More evidence needs to be gathered and evaluated,” she explained.

In the meantime, Allegranzi said, “the possibility of airborne transmission in public settings – especially closed, poorly ventilated settings – cannot be ruled out.”

Morawska said the evidence already exists. “A continuous surprise is that it takes the world such a long time to accept this, while this has such solid scientific foundation.” As an example, she cited an April report she coauthored in the journal Environment International. She and colleagues call for “national authorities to acknowledge the reality that the virus spreads through air and recommend that adequate control measures be implemented to prevent further spread of the SARS-CoV-2 virus, in particularly removal of the virus-laden droplets from indoor air by ventilation.”

The take-home message from the commentary, Morawska said, is a call to action. The authors state there is a need “to provide sufficient and effective ventilation (supply clean outdoor air, minimize recirculating air) particularly in public buildings, workplace environments, schools, hospitals, and aged care homes.”

WHO Chief Scientist Soumya Swaminathan, MD, explained why the organization remains cautious about making premature pronouncements regarding airborne transmission. “Any guidance we put out has implications for billions of people around the world, so we want to be as careful as possible,” she said during the press briefing. “We have to consider the weight of the evidence.”

“We are constantly looking for information on how we can do better,” Swaminathan added. WHO officials are reviewing hundreds of scientific reports every day, she said, and not all are of good quality. For this reason, she and other scientists at WHO perform a “living systematic review” – updating the consensus of evidence on a weekly basis.

“This process on COVID-19 will, I am sure, continue for the weeks and months to come,” she added.

This article first appeared on

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