The World Health Organization has recognized that there is new evidence that coronavirus can be spread by tiny airborne particles.
Airborne transmission could not be ruled out in crowded, closed, or poorly ventilated environments, said an official.
If the evidence is confirmed, this may affect the guidelines for interior spaces.
An open letter from more than 200 scientists had accused WHO of underestimating the possibility of airborne transmission.
WHO has so far declared that the virus is spread by droplets when people cough or sneeze.
“We wanted them to recognize the evidence,” Jose Jimenez, a chemist at the University of Colorado who signed the paper, told Reuters news agency.
“It is certainly not an attack on the WHO. This is scientific debate, but we felt we should go public because they refused to hear the evidence after many conversations with them, “he said.
WHO officials have warned that the evidence is preliminary and requires further assessment.
Benedetta Allegranzi, WHO technical manager for infection prevention and control, said that the evidence emerging from airborne transmission of the coronavirus in “the crowded, enclosed and poorly ventilated environments that has been described cannot be excluded “
A changing position?
Imogen Foulkes, BBC News in Geneva
For months, WHO has insisted that Covid-19 be transmitted via droplets emitted when people cough or sneeze. Droplets that do not linger in the air but fall on surfaces – this is why handwashing has been identified as a key preventative measure.
But 239 scientists from 32 countries disagree: they say there is strong evidence to suggest that the virus can also spread through the air: through much thinner particles that float for hours after the people speak or expire.
Today, WHO has admitted that there is evidence to suggest that this is possible in specific contexts, such as confined and overcrowded spaces.
This evidence will need to be carefully assessed, but if it is confirmed, the advice on how to prevent the spread of the virus may need to change and could lead to more widespread use of masks and more rigorous distancing, especially in bars, restaurants, and on public transportation.