The WHO said it is looking into the possibility that the coronavirus could spread through airborne microdroplets indoors.
An open letter signed by 239 scientists is calling on the World Health Organization (WHO), nations and healthcare bodies around the world to review established guidance on limiting the spread of Covid-19, which recommends physical distancing within two metres.
The letter – whose signatories include many who have worked with the WHO and on its committees – said that “there is every reason to expect” that SARS-CoV2 (the coronavirus that causes Covid-19) is transmissible across distances greater than two metres through airborne microdroplets less than five microns in diameter.
Current guidance suggests the virus is passed on via large droplets when someone sneezes or coughs. However, if microdroplets are confirmed as a means of transmission, it could mean someone talking, or even singing, would be enough to release it into the air.
However, the letter stresses that evidence so far suggests this potential threat may be limited to indoor spaces where microdroplets could travel tens of metres across a large, poorly ventilated room while settling from a height of 1.5 metres to the floor.
“It is understood that there is not as yet universal acceptance of airborne transmission of the coronavirus; but in our collective assessment there is more than enough supporting evidence so that the precautionary principle should apply,” they wrote.
“In order to control the pandemic, pending the availability of a vaccine, all routes of transmission must be interrupted.”
Ventilation is key
In response, the WHO’s technical lead for infection control, Benedetta Allegranzi, said that it will now look at all the evidence available on airborne transmission and release a new scientific brief in the coming days.
“We believe that we have to be open to this evidence and understand its implications regarding the modes of transmission and also regarding the precautions that need to be taken,” Allegranzi said.
If these findings are to be backed by near-unanimous scientific evidence, guidance on how we interact indoors could change.
In their letter, the scientists recommended a number of measures that should be taken to mitigate potential exposure. These include providing sufficient and effective ventilation, particularly in public buildings, workplace environments, schools, hospitals and elderly-care homes.
They also called for supplementing greater ventilation with further measures such as air filtration and germicidal ultraviolet lights. Unsurprisingly, overcrowding in spaces such as public transport or buildings should also be discouraged.
“Simple steps such as opening both doors and windows can dramatically increase air flow rates in many buildings,” they wrote.
“The measures we propose offer more benefits than potential downsides, even if they can only be partially implemented.”