The World Health Organisation is underplaying the airborne transmission potential of COVID-19, according to 239 scientists from across 32 countries. The scientists have penned an open letter, set to be published later this week, calling for the world’s foremost medical body to revise its recommendations and acknowledge that the virus may spread via aersols, particles smaller than respiratory droplets.
Till date, the WHO has maintained that the primary modes of transmission of the virus are via the inhalation of respiratory droplets released when individuals sneeze, cough, or speak, or via contact with surfaces that the virus may dwell on.
Respiratory droplets are larger and heavier particles that drop to the ground seconds after being projected. This is one of the key reasons why social distancing of between 3 and 6 feet has been recommended, and widely believed to be one of the most effective strategies to stop the spread of the virus.
Airborne transmission, on the other hand, involves particles known as droplet nuclei. These particles are much smaller than respiratory droplets and may linger and travel in the air for longer periods of time. Such droplets are also produced when people speak, sneeze or cough, but can also be produced through the evaporation of respiratory droplets. Droplet nuclei, or aerosols can float in the air, meaning that an environment that has been visited by a COVID-19 carrier could still remain dangerous even once the carrier has vacated it.
The scientists have noted that evidence from environments like meat processing plants suggests that airborne tranmission may, indeed, play a larger role in disease transmission than the WHO has declared. Representatives from the WHO have previously stated that airborne transmission was possible, but have downplayed its role as a primary mode of transmission.
Studies have shown airborne transmission is possible
In early June, researchers from the University of California San Diego, including Dr Mario J Molina, the winner of the 1995 Nobel Prize in Chemistry, published a paper in the journal, PNAS, that studied the progression of the outbreak in three major epicentres – Wuhan, New York City and Italy. The researchers noted that airborne transmission, ‘particularly via nascent aerosols,’ could be a dominant mode of transmission of the disease.
Another study looking into virus longevity, that sought to keep the aersolised virus airborne, found that the virus could remain active in the air for up to 16 hours. It is worth noting though, that this study did not take into account the effects of temperature, humidity or pollution on the surivival of the aerosolised virus.
The implications of aerosols as a primary route of transmission are significant. If, indeed, people are able to contract the virus via aersols, this may mean that face mask protocols may need to change such that individuals may need to wear them even indoors. What’s more, it also throws into question how effective social distancing may be, specifically if the virus is, not only able to survive for hours on end indoors, but also hover in the air, thereby increasing the risk of being inhaled or swallowed by individuals.
