More than 200 scientists have called for the World Health Organization and others to acknowledge that the coronavirus can spread in the air — a change that could alter some of the current measures being taken to stop the pandemic.

In a letter published this week in the journal Clinical Infectious Diseases, two scientists from Australia and the U.S. wrote that studies have shown “beyond any reasonable doubt that viruses are released during exhalation, talking and coughing in microdroplets small enough to remain aloft in the air.” That means people in certain indoor conditions could be at greater risk of being infected than was previously thought.

The scientists also state: “There is significant potential for inhalation exposure to viruses in microscopic respiratory droplets (microdroplets) at short to medium distances (up to several metres, or room scale), and we are advocating for the use of preventive measures to mitigate this route of airborne transmission”.

The WHO has long maintained that COVID-19 is spread via larger respiratory droplets, most often when people cough or sneeze, that fall to the ground. It has dismissed the possibility of airborne transmission, except for certain high-risk medical procedures, like when patients are first put on breathing machines. In a statement on Monday, the U.N. health agency said it was aware of the article and was reviewing it with technical experts.

The letter was endorsed by 239 scientists from a variety of fields. It stated that the issue of whether or not COVID-19 was airborne was of “heightened significance” as many countries stop restrictive lockdown measures.

The authors cited previous studies suggesting that germs closely related to the new virus were spread via airborne transmission. They said “there is every reason to expect” that the coronavirus behaves similarly. They also cited a Washington state choir practice and research about a poorly ventilated restaurant in Guangzhou, China, each of which raised the possibility of infections from airborne droplets.

The letter states: “The measures to be taken to mitigate airborne transmission risk include:

• Provide sufficient and effective ventilation (supply clean outdoor air, minimizing recirculating air) particularly in public buildings, workplace environments, schools, hospitals, and aged care homes.
• Supplement general ventilation with airborne infection controls such as local exhaust, high efficiency air filtration, and germicidal ultraviolet lights.
• Avoid overcrowding, particularly in public transport and public buildings.”

Reference:

Morawska, L. and D.K Milton. 2020. 239 Experts With One Big Claim: The Coronavirus Is Airborne. Clinical Infectious Diseases, ciaa939, https://doi.org/10.1093/cid/ciaa939

See also:

Apoorva Mandavilli. 2020. It is Time to Address Airborne Transmission of COVID-19. New York Times, https://www.nytimes.com/2020/07/04/health/239-experts-with-one-big-claim-the-coronavirus-is-airborne.html