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Critics say WHO's stance on "airborne" Covid-19 misses the mark

Droplets released by talking, sneezing or coughing contain a mix of large and smaller particles sols

More and more scientists believe that Covid-19 can be transmitted by an infected person's breath or speech, emitting tiny airborne virus particles that can travel meters. WHO now admits this can happen but is downplaying the risks.

In the past, becoming “airborne” was something that concerned us mostly when we were waiting for a flight to take off. Now, in the new Covid-19 normal, we are having to learn about the scientific use of the term.

Can the SARS-CoV-2 virus become “airborne” - meaning that tiny viral particles expelled by an infected person’s speech remain suspended in the air, circulating in poorly ventilated rooms, and sometimes landing in the eyes, nose or mouth of an unsuspecting restaurant patron or office mate meters away? Until just this week, WHO had staunchly maintained airborne virus transmission wasn’t a big risk with Covid-19. Now it is walking back on that position. But still too slowly, its critics say.

The scientific debate went airborne this week - after nearly 240 scientists published an open letter in the Clinical Journal of Infectious Diseases, criticizing WHO for downplaying the risks of airborne virus transmission. State the authors:

“There is significant potential for inhalation exposure to viruses in microscopic respiratory droplets (microdroplets) at short to medium distances (up to several meters, or room scale), and we are advocating for the use of preventive measures to mitigate this route of airborne transmission.”

Disease transmission by the smallest viral particles, called aerosols, is likely to be one of the main routes, the scientists maintain. They called on WHO to revise its technical guidelines that maintained the main transmission routes were liquid droplets, expelled by sneezing or coughs, and mostly infectious at a distance of a meter or less.

Why is this important? The potential for such tiny particles to travel so far explains why handwashing and social distancing at one meter has not been enough to stem the pandemic. More and more countries and cities are recognizing this too. Just this week, for instance, the Canton of Vaud, instituted a requirement for both employees and shoppers to wear masks in supermarkets and malls - irregardless of whether they are crowded or not. Such rules consider the likelihood that tiny viral particles may travel further and linger longer in the air than we previously thought. And as the experts explain, since so many people with Covid-19 are asymptomatic or mildly ill, there is no way to know who is infectious or not. But if everyone wears a mask, then those who are carrying the virus can’t become walking infection bombs - showering an invisible, but dangerous pathogen on others.

Figure illustrating how aerosol virus particles circulate in a poorly ventilated room (above), and one with an open window (below) (Source: Clin Jour Infectious Diseases)

Progress - but not enough? On Wednesday, WHO finally acknowledged the “airborne” route may be a factor to consider - although it still maintains that it’s not the main transmission route. The new WHO brief also remains focused on risks of transmisison in crowding of one meter or less. It hus also falls short of making stronger recommendations for public use of masks. This is something that critics have wanted to hear from the global organization - whose guidelines are heeded worldwide. Donald Milton, a respiratory virus expert at the University of Maryland, and one of the co-authors of the open scientific letter, summed it up like this on his Twitter page:

“First — the good. WHO included the recommendations to “Avoid … enclosed spaces with POOR VENTILATION;” and that we should “ENSURE GOOD VENTILATION in indoor settings, including homes and offices.” I’m really happy to see this.

“But… they only recommend face masks when within one meter of other people. This is very bad advice, especially in “enclosed spaces with poor ventilation. This terrible recommendation comes from the fundamental problem with the new WHO “scientific brief;” they do not use fact-based science to define “respiratory droplets” and “aerosols.”

The WHO hesitancy on masks, Milton and others say, is anchored in outdated science about virus particles and how far they can travel. Other coronaviruses, like the one that causes SARS, are known to travel, and be infectious, at distances of more than a meter, and mounting evidence indicates the new coronavirus behaves in the same way. Milton:

“The extensive research and tremendous progress in the physics and biology of aerosols since 1940 appears to have had no impact. The contention that “respiratory droplets” in the size range of >5 to 10 µm [microns] in diameter only travel up to 1 meter is absolutely wrong.”


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