WHO has formally acknowledged the possibility that the novel coronavirus can remain in the air in crowded indoor spaces, where “short-range aerosol transmission… cannot be ruled out”. The updated brief has come three days after a group of 239 scientists from 32 countries published a commentary titled ‘It is Time to Address Airborne Transmission of COVID-19’, in which they issued an “appeal to the medical community and to the relevant national and international bodies to recognize the potential for airborne spread of COVID-19”.

So, what has the WHO said in its updated brief?

Referring to several recent studies, the WHO has said that some outbreaks that have occurred in crowded indoor spaces suggest “the possibility of aerosol transmission”, although “combined with droplet transmission”. Such situations have arisen “during choir practice, in restaurants or in fitness classes”.

According to the WHO, “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”.

There is, however, a caveat — the WHO does not think that even in these situations, the virus was transmitted exclusively by the aerial route.

The WHO brief still says that “the detailed investigations of these clusters suggest that droplet and fomite transmission could also explain human-to-human transmission within these clusters”.

Transmission through respiratory droplets — when an infected person coughs, sneezes, talks, or sings — is still understood to be the primary mode of transmission of the virus.