The World Health Organization (WHO) is acknowledging there is "evidence emerging" of coronavirus spreading through the air.
The WHO has previously said the virus that causes COVID-19 spreads primarily through small droplets expelled from the nose and mouth of an infected person, that quickly sinks to the ground.
But in an open letter published this week,
239 scientists in 32 countries outlined evidence that they say shows floating virus particles can infect people who breathe them in.
Because those smaller exhaled particles can linger in the air, the scientists in the group have been urging the WHO to update its guidance.
"We have been talking about the possibility of airborne transmission and aerosol transmission as one of the modes of transmission of COVID-19," Maria Van Kerkhove, WHO's technical lead on COVID-19, said.
The change in guidance was also mentioned by Benedetta Allegranzi, the WHO's technical lead for infection prevention and control.
She said there was evidence emerging of airborne transmission of the coronavirus, but that it was not definitive.
"The possibility of airborne transmission in public settings — especially in very specific conditions, crowded, closed, poorly ventilated settings that have been described, cannot be ruled out," she said.
"However, the evidence needs to be gathered and interpreted, and we continue to support this."
There is growing evidence that small droplet (airborne) transmission is a significant route of infection indoors.(Supplied: Airborne transmission of SARS-CoV-2 By Lidia Morawska)
The new acknowledgement will force a change in the advice the WHO gives about how to stop the pandemic.
Dr Van Kerkhove said the WHO would publish a scientific brief summarising modes of transmission of the virus in the coming days.
"A comprehensive package of interventions is required to be able to stop transmission," she said.
"This includes not only physical distancing, it includes the use of masks where appropriate in certain settings, specifically where you can't do physical distancing and especially for healthcare workers."
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Professor Lidia Morawska says viruses can last in the air for tens of minutes and potentially hours.
Jose Jimenez, a chemist at the University of Colorado, was one of the 239 who signed the open letter that prompted the WHO's change of heart.
He said many health professionals can be worried about acknowledging airborne transmission, for fear of creating a panic.
"If people hear 'airborne', healthcare workers will refuse to go to the hospital," he said.
He also said this fear could lead to people buying up highly protective respirator masks, "and there will be none left for developing countries".
Despite this, he said it was important for WHO to look at the evidence out there that could indicate coronavirus can be spread through the air.
"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.
The open letter published this week calls for WHO to investigate the possibility the disease can be transmitted through the air.
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