Why does the WHO not recognize the transmission of the coronavirus via aerosols?

Even the US CDCs say airborne transmission of the coronavirus is possible, yet the WHO still claims there is not enough confirmation. What's missing?

(image: Getty Images) A ​​few weeks ago we told you about the ballet of the US Centers for Disease Control and Prevention (CDC) that first publish an update on the transmission modes of the coronavirus highlighting the possibility of transmission aerial (airborne), and then withdraw it. A mistake, they say: an unrevised draft that had not yet been published.

Now that draft, perhaps a little sweetened, is back online. Based on growing scientific evidence, CDC experts recognize that the mode of airborne transmission (more than a meter away) via aerosols (droplets smaller than 5 microns) of the coronavirus is possible, although rarer than direct contact. with an infected person or via droplet. The conditions for airborne diffusion would be closed spaces, inadequately ventilated and crowded.

In short, more and more national organizations and world experts put their support on the airborne issue, thus finding themselves in disagreement with the World Health Organization (WHO ), reluctant to update its guidelines. What blocks it?

Increasing evidence of airborne transmission

As early as July 239 scientists had urged WHO to change their point of view in a letter, pointing out that the evidence of air transmission of SARS-Cov-2 were accumulating. And today some of them increase the dose, with a new letter published in Science.

"There is overwhelming evidence that this is an important transmission route for Covid-19, and we desperately need federal guidance in this direction," aerosol expert Linsey Marr told the Washington Post at Virginia Tech and among the authors of the letter in Science. "I would like to point out that short-range airborne transmission when people are in close contact, ie inhalation of aerosols, is probably more important than transmission by large droplets that are sprayed on mucous membranes."

According to these scientists, there are well-documented cases where the coronavirus has spread widely and rapidly in an enclosed environment: a restaurant in Guangzhou, China, a bus in the Chinese province of Zhejiang, a call center in Seoul, a choir in Washington state (where one member infected more than 50 people). Episodes that CDC experts have deemed sufficient to change their guidelines.

Aerosols and airborne transmission "are the only way to explain the super-diffusion events we are seeing," added al Washington Post Kimberly Prather of the University of California at San Diego, also among the authors of the new paper. According to the expert, once the airway is officially recognized it will become a problem that can be solved through adequate ventilation and always wearing masks indoors. Because a safe social distance does not exist in closed environments.

WHO reticence: reasons and criticisms

As Benedetta Allegranzi, technical manager of the sector dedicated to the control of infections of the 'WHO, the organization does not deny that the coronavirus can also spread by air via aerosols beyond the safety distance currently recommended. However, he argues that from a scientific point of view the evidence is still insufficient: the conditions under which airborne transmission would occur would be particular and rarer, and scientists have not yet been able to replicate them to study the dynamics of diffusion. A too rigid and medicalized vision according to many experts, who also contest the WHO's definitions of airborne and aerosol, considering them formal and ultimately fictitious.

But this would not be the only thing to hold back WHO. According to Paul Hunter of the University of East Anglia in Great Britain, the organization must take into account geopolitical issues. The guidelines are aimed at every country in the world and not all have the same resources: shifting attention to a mode of transmission currently considered less decisive could lead to the migration of those few resources in low and middle-income states.

Even this motivation, however, is subject to criticism from some international experts, who consider the attitude of the WHO to be somewhat paternalistic.