Early in the coronavirus pandemic, a team of scientists called on the World Health Organization to recognize that the disease could be transmitted through the air.
Officials initially rejected such requests despite growing evidence that coronavirus-laden droplets are in the air and indoor spaces are breeding grounds for infection. Researchers responded with a public campaign that helped persuade the World Health Organization to finally acknowledge that the coronavirus was airborne in late 2021.
In response to the controversy, the agency also asked a panel of advisors, including some scientific commentators, to update formal guidelines for classifying how pathogens spread. After more than two years of discussion, the group has published a new definition that could have significant implications for countries around the world that rely on authorities to develop policies to curb the spread of the disease. announced.
The WHO's previous position has been that only a handful of pathogens, such as tuberculosis, can be considered airborne and can be transmitted over long distances in tiny droplets. But the new report suggests a broader category that doesn't depend on droplet size or distance spread. Such changes sparked debate as they raised the prospect that more diseases could require costly control measures, such as hospital isolation rooms and protective equipment.
“This is an important first step,” said Dr. Ed Nadel, a tuberculosis expert at Harvard Medical School and a member of the group. “We really got off to a good start with the agreed terms, even if everyone wasn’t happy with it.”
Before the pandemic, the WHO and other agencies generally recognized several ways in which diseases could spread. One is through “contact transmission,” where someone transmits the pathogen through direct contact with an infected person or through contact with a contaminated surface.
“Droplet transmission” is when the disease is transmitted over a short distance when people cough or sneeze and droplets larger than 5 microns (5 millionths of a meter) land directly on the victim's mouth, eyes, or nose. It refers to spreading.
“Airborne” refers to a handful of diseases that spread in droplets smaller than 5 microns and can float long distances until someone inhales them.
When the new coronavirus emerged, authorities said it was likely spread over close distances through contact or droplet transmission.
But Li Yu-Kuo, a mechanical engineer at the University of Hong Kong, and many other critics worried that the WHO was overlooking the possibility that the coronavirus could be transmitted through the air. As the pandemic progressed, scientists found evidence in outbreaks that the coronavirus can indeed spread over long distances as airborne droplets. (Some scientists have questioned the validity of these studies.)
WHO established a new advisory group in November 2021 and asked Dr. Lee to co-chair it. At the group's meeting, Dr. Lee and others argued that authorities were relying on a false dichotomy.
For example, there is little scientific basis for the 5 micron threshold for small droplets. Larger droplets can also remain suspended for long periods of time.
The researchers also argued that close-range transmission is not evidence that the disease can be spread by coughing or sneezing alone. Infected people exhale droplets when they breathe or talk, which can be inhaled by people nearby.
The new report separates transmission routes into contact routes and airborne routes. The group agreed to call the second route “airborne.”
Lindsey Marr, an environmental engineer at Virginia Tech and a member of the advisory group, found this language more troublesome than simpler terms like airborne transmission.
“I think it’s very clunky,” she said. “But we were looking for a lowest common denominator term that everyone could use.”
The report further specifies that pathogens can be spread through the air in two ways. The first is “direct deposition,” which refers to droplets hitting the mucous membranes of the mouth, eyes, and nose. The other is “airborne infection/inhalation,'' where you breathe in droplets.
After scientists came up with the new term, the WHO received agreement from the US Centers for Disease Control and Prevention and its counterparts in Africa, China and Europe to adopt the same definition.
“This is a very important statement of agreement to work together,” said WHO chief scientist Dr Jeremy Farrar.
However, the new report makes no recommendations on how authorities should stop the spread of the disease through these different routes. The authors acknowledged that they were unable to reach a consensus on this issue.
Traditionally, hospital guidelines for managing airborne diseases have called for costly measures such as negative-pressure isolation rooms and the installation of N95 masks and other protective equipment to avoid inhaling tiny droplets. I did. However, it is not clear what diseases require such management or what efforts are needed outside the hospital.
Dr. Walter Zing, an infectious disease expert at the University of Zurich and a member of the advisory group, said the older categories provided more direct guidance. For example, it was once thought that staying several feet away from someone who was coughing or sneezing was an effective way to avoid droplet infection.
“It's too simple and in some ways probably not true, but it served its purpose,” he said. “Now we need to bring other variables to the table.”
Dr. Farrar said such guidelines should be based on clear experimental evidence, but for many diseases that evidence is still lacking. For example, scientists are still debating the extent to which influenza, which has been studied for more than a century, is airborne.
“We know something, but we're not completely sure,” Dr. Farrar said. “That's the kind of work we desperately need in our flu response.”