World Health Organization Redefines Airborne Pathogens Terminology

In a bid to avoid the confusion that trailed the COVID-19 pandemic, the World Health Organization (WHO) and about 500 experts have jointly agreed for the first time to redefine what it means to say a disease is spread through the air. The WHO believes that the clarification would help save lives in the future.

The technical document on the matter was released by the WHO on Thursday, April 18, 2024. The Geneva-based United Nations health agency said it was the first step towards forging a better preventive measure for airborne pathogens, both for diseases already in existence like measles and future pandemic threats.

In the new document, the term “through the air’ is now accepted as a descriptor for an infectious disease where the primary means of transmission involves the movement of the pathogen through the air or being suspended in the air. The new descriptor is in line with terms like “waterborne” diseases which are clearly understood by the public and across disciplines.

The new document is moving away from “aerosols” and “droplets”

In the past, agencies would demand a high level of proof before designating a disease as airborne—and they required stringent containment measures. In the new document, the risk of exposure and severity of disease are considered.

Nearly 500 experts contributed to the new definition including public health professionals, physicists, and engineers. Some of them had disagreed on the topic in the past, unable to reach a consensus on whether infectious particles were aerosols or droplets based on size. Moving away from designation based on size has made it easier for them to reach an agreement. 

Around 200 scientists said the WHO failed to warn people about the risk of the virus spreading through the air in the early days of the COVID-19 pandemic. The scientists claimed that this led to an overemphasis on handwashing as a preventive measure rather than ventilation. 

When evidence started emerging around July 2020 of airborne spread, the then chief scientist Soumya Swaminathan later said the WHO should have been more forceful “much earlier”. Swaminathan later began the process to get a definition.

Why the new terminology is important

Jeremy Farrar who succeeded Swaminathan said in an interview that the new definition goes beyond COVID-19. Farrar noted that at the beginning of the pandemic, there was a lack of evidence and that the WHO acted in “good faith”. At that time, Farrar was the head of the Wellcome Trust charity and advised the British government on the pandemic.

According to Farrar, getting a definition that experts across different disciplines accept will pave the way for discussions to begin on things like ventilation in settings like schools and hospitals. 

Farrar compared the new definition to the time when it was discovered that blood-borne viruses like hepatitis B and HIV could be spread by medics who did not wear gloves during procedures. This also explains the importance of constantly reviewing scientific knowledge.

“When I started out, medical students, nurses, doctors, none of us wore gloves to take blood,” Farrar told Reuters. “Now it is unthinkable that you wouldn’t wear gloves. But that came because everyone agreed on what the issue was, they agreed on the terminology.”