GENEVA — Airborne transmission of the novel coronavirus (COVID-19) can occur during medical procedures that generate aerosols, Reuters quoted the World Health Organization (WHO) as saying Friday.

The organization further said some outbreak reports related to indoor crowded spaces have suggested the possibility of aerosol transmission, combined with droplet transmission, such as during choir practice, in restaurants or in fitness classes.

The WHO on Tuesday acknowledged "emerging evidence" of the airborne spread of the novel coronavirus, after a group of scientists urged the global body to update its guidance on how the respiratory disease spread.

An open letter from more than 200 scientists had accused the WHO of underestimating the possibility of airborne transmission. The WHO has so far said that the virus is transmitted through droplets when people cough or sneeze.

The WHO published new guidance Thursday, saying it can’t rule out the possibility that the coronavirus can be transmitted through air particles in closed spaces indoors, including in gyms and restaurants.

The WHO previously acknowledged that the virus may become airborne in certain environments, such as during “medical procedures that generate aerosols.”

The new guidance recognizes some research that suggests the virus may be able to spread through particles in the air in “indoor crowded spaces.” It cited “choir practice, in restaurants or in fitness classes” as possible areas of airborne transmission.

“In these events, short-range aerosol transmission, particularly in specific indoor locations, such as crowded and inadequately ventilated spaces over a prolonged period of time with infected persons cannot be ruled out,” the United Nations health agency’s new guidance said.

The WHO said in its guidance that while early evidence suggests the possibility of airborne transmission in such environments, spread by droplets and surfaces could also explain transmission in those cases.

“However, the detailed investigations of these clusters suggest that droplet and fomite transmission could also explain human-to-human transmission within these clusters,” the guidance said.

The WHO added that more research is needed to further investigate preliminary findings. The agency said the main mode of transmission is still believed to be through respiratory droplets. — SPA/Agencies