The World Health Organization has acknowledged there’s emerging evidence that the coronavirus can be spread by tiny particles suspended in the air.
The airborne transmission cannot be ruled out in crowded, closed or defectively ventilated settings, an official said.
If the evidence is confirmed, it could affect directions for indoor spaces.
An open letter from more than 200 scientists had accused the WHO of underestimating the chance of airborne transmission.
The WHO has up to now said that the virus is transmitted through droplets when people cough or sneeze.
“We wanted them to acknowledge the evidence,” Jose Jimenez, a chemist at the University of Colorado who signed the paper, told the Reuters news agency.
“This is definitely not an attack on the WHO. It’s a scientific debate, but we felt we needed to go public because they were refusing to hear the evidence after many conversations with them,” he said.
Another signatory – Professor Benjamin Cowling of Hong Kong University – told the BBC the finding had “important implications”.
“In healthcare settings, if aerosol transmission poses a risk then we understand healthcare workers should really be wearing the best possible preventive equipment… and actually the World Health Organization said that one of the reasons they were not keen to talk about aerosol transmission of Covid-19 is because there’s not a sufficient number of these kind of specialised masks for many parts of the world,” he said.
“And in the community, if we’re thinking about aerosol transmission being a particular risk, then we need to think about how to prevent larger super spreading events, larger outbreaks and those occur in indoor environments with poor ventilation, with crowding and with prolonged close contact.”
WHO officials have cautioned the evidence is preliminary and requires further assessment.
Benedetta Allegranzi, the WHO’s technical lead for disease prevention and control, said that evidence emerging of airborne transmission of the coronavirus in “crowded, closed, poorly ventilated settings that have been described, cannot be ruled out”.
A shifting position?
Imogen Foulkes, BBC News in Geneva
For months, the WHO has insisted that Covid-19 is transmitted via droplets emitted when people cough or sneeze. Droplets that not linger in the air, but fall onto surfaces – that’s why handwashing has been identified as a vital prevention measure.
But 239 boffins from 32 countries do not agree: they do say there is strong evidence to suggest the herpes virus can also spread in the air: through much tinier particles that float around for hours after people talk, or breathe out.
Today the WHO admitted there was evidence to suggest this was possible in specific settings, such as for example enclosed and crowded spaces.
That evidence must be thoroughly evaluated, but if it is confirmed, the suggestions about how to prevent the herpes virus spreading may need to change, and might lead to more widespread usage of masks, and much more rigorous distancing, especially in bars, restaurants, and on public transport.