Further to Scientist calling for the World Health Organization (WHO) to revise their recommendations, WHO has expanded its coronavirus guidance to include the possibility in certain circumstances of airborne transmission, in which the virus could be spread through tiny droplets that linger in the air.
The update came Thursday after an open letter signed by more than 200 scientists pressed the agency this week to acknowledge the potential role that tiny droplets, or aerosols, play in airborne transmissions among people in crowded, indoor settings for prolonged periods.
“There have been reported outbreaks of COVID-19 in some closed settings, such as restaurants, nightclubs, places of worship or places of work where people maybe shouting, talking, or singing,” the WHO said in its updated review of the evidence. “In these outbreaks, aerosol transmission, particularly in these indoor locations where there are crowded and inadequately ventilated spaces where infected persons spend long periods with others, cannot be ruled out.”
The agency said more research is “urgently needed to investigate such instances and assess their significance for transmission of COVID-19.”
The WHO’s expanded guidance on the airborne transmission is notable, but experts maintain that aerosols are likely to be just a small part of how the coronavirus spreads and that close contact with an infected person is still the most common source of transmission.
“You can put all these definitions in place, but we’ve always been concerned about spread when people are in small spaces, indoors, for long periods,” said Cindy Prins, an epidemiologist at the University of Florida in Gainesville.
For respiratory illnesses like COVID-19, the disease caused by the coronavirus, the medical community focuses on two primary ways that the virus can spread: airborne transmission and what’s known as droplet transmission.
With droplet transmission, it’s thought that virus-filled particles can be ejected from the mouth or the nose when a person speaks, coughs or sneezes. The droplets can be flung through the air — up to 6 feet from the infected person — but then drop to the ground or onto other surfaces fairly quickly if they don’t come into contact with other people nearby.
Airborne transmission, on the other hand, occurs when tiny aerosol particles are expelled by talking, sneezing, or coughing but then remain suspended in the air. The minuscule particles can also travel away from an infected person by floating on air currents.
Measles, chickenpox, and tuberculosis are other diseases that can spread through airborne transmission.
When asked about airborne spread of coronavirus, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases said, “There’s no solid evidence that that type of transmission is occurring.”
But he added, “We can’t rule it out completely.”
While airborne and droplet transmission are different, they aren’t mutually exclusive, said Dr. Isaac Bogoch, an infectious disease physician who is an associate professor of medicine at the University of Toronto.
“We often think about these clinical definitions as silos, but that’s not entirely accurate,” Bogoch said. “There’s a spectrum — from droplets to airborne. When we think about COVID-19, there may be some airborne transmission, but it’s safe to say that the majority of transmission falls toward the droplet side of the spectrum.”
“Everyone should wear a mask”.
Bogoch pointed to hospital protocols as a key indicator that airborne transmissions are likely to be rare. When treating coronavirus patients, most hospitals have been adhering to infection control guidelines tailored to droplet transmission, rather than the more stringent procedures to protect against airborne infections.
If COVID-19 was truly airborne, Bogoch said, infection rates among health care workers would have skyrocketed.