Science Policy Around the Web – May 9, 2024

COVID-19 Prompts WHO to Reclassify Pathogen Transmission Categories

Bianca Nogrady, a freelance journalist, details in her recent Nature article the idiosyncrasies of the terminology used to define methods of pathogen spread. At the beginning of the COVID-19 pandemic, the WHO used terminology that distinguished between “droplets” (particles of five millimeters in diameter or greater) and “aerosols” (particles of less than five millimeters in diameter). The discovery of SARS-CoV-2 particles that were greater than 5 mm in diameter led to the hypothesis that this virus was predominantly spread by deposition of large particles onto surfaces, after which point another person could contact them. Later information, however, indicated that SARS-CoV-2 could also be spread via aerosolization, meaning that there was a risk of airborne transmission as well.

??????????????? These transmission criteria were reevaluated in a recent WHO report that took two years to prepare. Despite the lengthy assessment that took place, many scientists still believe that the classification criteria are too imprecise. While the particle size distinctions that led to confusion during the COVID-19 pandemic were done away with, some interviewees took issue with the decision to use the term “through the air” to describe the mode of transmission of pathogens that they would prefer to describe as having an “airborne” mode of transmission. Within the new “through the air” category are two subclassifications: “airborne transmission/inhalation” and “direct deposition”, which are distinguished by whether the droplets are capable of remaining suspended in the air for extended periods of time or simply travel from one host to another via something like a cough or sneeze. While the new classification may leave room for improvement, most scientists are confident that these revisions will prevent misclassification of pathogens like SARS-CoV-2 and lead to preemptive actions such as masking and ventilation during outbreaks that slow the spread of transmission.

Original article by Bianca Nogrady, Science

Article Summary by Josephine Trichka, B.A.