The World Health Organisation has updated its guidelines on how the coronavirus is transmitted, stating that the likelihood that the virus can go airborne, particularly in enclosed spaces like restaurants and gyms, “cannot be ruled out.”
In its updated guidelines issued on Thursday, the WHO cited multiple reported outbreaks of Covid-19 involving people who became infected after being in crowded indoor spaces, including fitness classes and choir practice.
“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 WHO concluded while acknowledging that more research is needed.
The organisation had previously refrained from including airborne transmission among the virus’s potential modes of transmission among the general public. It did state that airborne transmission “may be possible” in specific medical settings and circumstances that involved aerosol-generating treatments.
WHO Chief Scientist Dr Soumya Swaminathan said in an interview with India Today on Wednesday that there’s still no concrete proof that airborne transmission of the coronavirus is happening, but there are enough reported instances of its spread in closed settings to warrant proper attention and extra precautions.
These precautions include wearing a mask and trying to avoid relatively small enclosed places, like bars and clubs. This is because respiratory droplets that are less than 5 microns in size, called droplet nuclei or aerosols, “can stay in the air for a little bit of time and they can take a little longer to settle on the ground,” Swaminathan said. “These particles could be inhaled by other people who are in the vicinity, in the room, and this could be called airborne transmission.”
Fortunately, the virus does not appear to be truly airborne, like the measles virus is. If it were, far more people would have become infected, she said.
The WHO’s listed modes of coronavirus transmission also include droplet transmission, which occurs when a person is in close contact with someone with respiratory symptoms, and fomite transmission, which happens when someone becomes infected by touching a surface that had recently been touched by an infected person.
To date, there have not been any confirmed instances of fomite transmission but there is consistent evidence of it being possible because the virus is able to contaminate and survive on certain surfaces, the WHO guidelines state.
As of Thursday, the US Centers for Disease Control and Prevention did not have airborne transmission on its list of ways the virus can spread. It does acknowledge that the virus is “spreading more efficiently than influenza, but not as efficiently as measles.”
“In general, the more closely a person interacts with others and the longer that interaction, the higher the risk of Covid-19 spread,” the CDC website states.