Till now, WHO has downplayed airborne transmission of COVID-19. WHO has been insisting that COVID-19 spreads predominantly through large respiratory droplets — the ones that come flying out of our mouths when we cough, sneeze and speak but then quickly fall to the ground.
But now 239 scientists from 32 different countries and many different areas of science (including virology, aerosol physics and epidemiology) have penned an open letter urging the WHO to change their advice.
“We ignore COVID-19 airborne spread indoors at our peril,” the scientists say.
If their plea is heard, the ways in which the world attempts to control the virus could change dramatically.
Led by internationally recognized air quality and health expert QUT Professor Lidia Morawska, the appeal is to address the overwhelming research finding that an infected person exhales airborne virus droplets when breathing and talking that can travel further than the current 1.5m social distance requirement.
“Studies by the signatories and other scientists have demonstrated beyond any reasonable doubt that viruses are exhaled in microdroplets small enough to remain aloft in the air and pose a risk of exposure beyond 1 to 2m by an infected person,” Professor Morawska, director of the International Air Quality and Health Laboratory, said.
Airborne Transmission
At typical indoor air velocities, a 5-micron droplet will travel tens of meters, much greater than the scale of a typical room while settling from a height of 1.5m above the floor.
The measures that need to be taken to mitigate airborne transmission include:
- Provide sufficient and effective ventilation (supply clean outdoor air, minimize recirculating air) particularly in public buildings, workplace environments, schools, hospitals, and aged care homes.
- Supplement general ventilation with airborne infection controls such as local exhaust, high efficiency air filtration, and germicidal ultraviolet lights.
- Avoid overcrowding, particularly in public transport and public buildings.
“These are practical and can be easily implemented and many are not costly. For example, simple steps such as opening both doors and windows can dramatically increase air flow rates in many buildings. Numerous health authorities currently focus on hand-washing, maintaining social distancing, and droplet precautions. Hand-washing and social distancing are appropriate, but it is view, insufficient to provide protection from virus-carrying respiratory microdroplets released into the air by infected people.”
What does the WHO say?
In the latest interim guidance, the WHO said current evidence suggests COVID-19 is primarily spread through large droplet transmission when people are within 1 metre of each other.
It also warns that transmission may occur through fomites (inanimate surfaces or objects) however experts believe that risk is quite low.
The WHO says more research is required to determine the risk of airborne transmission in other environments.
“High quality research including randomised trials in multiple settings are required to address many of the acknowledged research gaps,” the WHO said in their latest advice on masks.
