WHO Adopts New Airborne Disease Definition

Super-high magnification of coronavirus particles (like the current SARS-CoV-2 pandemic) spread through tiny droplets of liquid (aerosols) floating through the air. Illustration for means of transmission: droplet and aerosolized infection | Image by fpm/Getty Images

After much debate during the COVID-19 pandemic, the World Health Organization has now broadened its definition of airborne pathogens to include droplets of any size that either land directly on a person or are inhaled through the air.

The WHO update comes after extensive discussions and controversies surrounding the classification of COVID-19 transmission. Initially, WHO resisted acknowledging COVID as an airborne disease despite mounting evidence suggesting its ability to linger in the air indoors, leading to infections. WHO’s initial position was that COVID-19 was likely spread only over short distances by direct contact or droplet transmission on a person.

However, persistent advocacy from scientists eventually prompted WHO to update its classification in late 2021, recognizing COVID as airborne, per The New York Times.

In response to the COVID controversy and to address broader concerns, the WHO assembled a group of advisers, including critics, to revise its guidelines for classifying how pathogens spread. The result is a new report outlining updated definitions that could have significant implications for global disease control policies.

The updated classification divides transmission routes into those involving contact and those involving the air. The latter is now referred to as “through the air transmission,” encompassing both direct deposition onto mucous membranes and the inhalation of airborne droplets of any size. This shift raises concerns about potentially imposing costly control measures for a wider range of diseases, according to the NYT.

According to the NYT, if this classification had been in use at the start of the pandemic, it could have led to immediate recommendations for the use of high-quality masks, prioritization of indoor ventilation, and potentially less emphasis on social distancing.

Linsey Marr, an aerosol scientist and professor at Virginia Tech and a member of the WHO consultation group behind the new report, said the report will “enable clearer communication with the public about the transmission of pathogens and how to reduce the risk of transmission.” 

“Prior to this, a flawed understanding of airborne transmission of infectious diseases caused a lot of miscommunication about how COVID-19 was transmitted and how people could best protect themselves. For example, wiping down groceries was not a good use of our time,” Marr said, per CNN. 

“Public health agencies were hesitant to use the word ‘airborne’ because of differences in understanding among experts about what it meant. I hope that this report will allow public health communicators to use the word ‘airborne’ because this word is the simplest and clearest way to explain to the average person how a disease might be transmitted.”

While the agreement on terminology marks progress, there remains uncertainty about how measures. Traditional guidelines for airborne diseases recommend costly measures such as isolation rooms and protective gear, but determining which diseases warrant such precautions remains challenging.

Despite the lack of consensus on control measures, the adoption of standardized definitions by international health agencies signals a step towards unified efforts in disease prevention and control. 

Stephen S. Morse, a professor of epidemiology at Columbia University Mailman School of Public Health, acknowledged that the clarified terminology in the report “is an improvement,” but he questioned whether it would have made a difference in managing the pandemic. 

“There were many failures in dealing with the pandemic; it would have been useful to have greater clarity, but I don’t think it would have made a great difference overall. It would have helped people to better protect themselves, but we didn’t have appropriate personal protective equipment available anyway,” Morse said. 

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