I find this Wired article an important exploration of an enormous wrong cached belief in the medical establishment: namely that based on its size, Covid would be transmitted exclusively via droplets (which quickly fall to the ground), rather than aerosols (which hang in the air). This justified a bunch of extremely costly Covid policy decisions and recommendations: like the endless exhortations to disinfect everything and to wash hands all the time. Or the misguided attempt to protect people from Covid by closing public parks and playgrounds, which pushed people to socialize indoors instead.[1]
According to the medical canon, nearly all respiratory infections transmit through coughs or sneezes: Whenever a sick person hacks, bacteria and viruses spray out like bullets from a gun, quickly falling and sticking to any surface within a blast radius of 3 to 6 feet. If these droplets alight on a nose or mouth (or on a hand that then touches the face), they can cause an infection. Only a few diseases were thought to break this droplet rule. Measles and tuberculosis transmit a different way; they’re described as “airborne.” Those pathogens travel inside aerosols, microscopic particles that can stay suspended for hours and travel longer distances. They can spread when contagious people simply breathe.
The distinction between droplet and airborne transmission has enormous consequences. To combat droplets, a leading precaution is to wash hands frequently with soap and water. To fight infectious aerosols, the air itself is the enemy. In hospitals, that means expensive isolation wards and N95 masks for all medical staff.
Finally, here’s a 2006 paper by Lidia Morawska, who features prominently in the article, on droplet transmission:
This paper reviews the state of knowledge regarding mechanisms of droplet spread and solutions available to minimize the spread and prevent infections.
Practical implications: Every day tens of millions of people worldwide suffer from viral infections of different severity at immense economic cost. There is, however, only minimal understanding of the dynamics of virus-laden aerosols, and so the ability to control and prevent virus spread is severely reduced, as was clearly demonstrated during the recent severe acute respiratory syndrome epidemic. This paper proposes the direction to significantly advance fundamental and applied knowledge of the pathways of viral infection spread in indoor atmospheric systems, through a comprehensive multidisciplinary approach and application of state-of-the-art scientific methods. Knowledge gained will have the potential to bring unprecedented economical gains worldwide by minimizing/reducing the spread of disease.
This potential proved harder to realize than expected.
On Trusting the Experts
This story is one of the lessons from the Covid years which I come back to most often. The screw-up informs how I think about questions of expertise, like to which extent I can trust experts and whether experiences from the Covid pandemic should reduce that trust.[2]
And what does it even mean to “trust the experts”, when there are multiple factions which claim expertise on a topic?
From the article, about a Zoom meeting in April 3, 2020:
[The] new coronavirus looked as if it could hang in the air, infecting anyone who breathed in enough of it… But the WHO didn’t seem to have caught on. Just days before, the organization had tweeted “FACT: #COVID19 is NOT airborne.” That’s why … [36 aerosol scientists were] trying to warn the WHO it was making a big mistake.
Over Zoom, they laid out the case. They ticked through a growing list of superspreading events in restaurants, call centers, cruise ships, and a choir rehearsal, instances where people got sick even when they were across the room from a contagious person. The incidents contradicted the WHO’s main safety guidelines of keeping 3 to 6 feet of distance between people and frequent handwashing. If SARS-CoV-2 traveled only in large droplets that immediately fell to the ground, as the WHO was saying, then wouldn’t the distancing and the handwashing have prevented such outbreaks? Infectious air was the more likely culprit, they argued. But the WHO’s experts appeared to be unmoved. If they were going to call Covid-19 airborne, they wanted more direct evidence—proof, which could take months to gather, that the virus was abundant in the air. Meanwhile, thousands of people were falling ill every day.
On the video call, tensions rose. At one point, Lidia Morawska, a revered atmospheric physicist who had arranged the meeting, tried to explain how far infectious particles of different sizes could potentially travel. One of the WHO experts abruptly cut her off, telling her she was wrong, Marr recalls. His rudeness shocked her...
Morawska had spent more than two decades advising a different branch of the WHO on the impacts of air pollution. When it came to flecks of soot and ash belched out by smokestacks and tailpipes, the organization readily accepted the physics she was describing—that particles of many sizes can hang aloft, travel far, and be inhaled. Now, though, the WHO’s advisers seemed to be saying those same laws didn’t apply to virus-laced respiratory particles. To them, the word airborne only applied to particles smaller than 5 microns. Trapped in their group-specific jargon, the two camps on Zoom literally couldn’t understand one another.
So the article obviously takes the side of the aerosol scientists, including calling one “revered”, and calling a WHO expert “rude”. And given that the WHO eventually relented on this issue[3], that makes sense. But an article which takes sides more than a year after the fact doesn’t help us as much to decide which experts to trust in the moment.
That being said, when a big organisation like the WHO makes factual claims with far-reaching economic consequences, and is then very slow to change its mind, and to my knowledge neither apologizes for the mistakes nor fires or even just reprimands anyone responsible, that certainly makes me trust it a lot less.
Conversely, I studied physics, so I can just follow my own tribal instincts and decide to trust the physicists over the doctors.
Maybe it’s easy to decide which experts to trust, after all!
I wonder how a what-if scenario would’ve worked out where everything about Covid stayed the same, except that this cached belief had been corrected before 2020.
… short-range aerosol transmission, particularly in specific indoor locations, such as crowded and inadequately ventilated spaces over a prolonged period of time with infected persons cannot be ruled out.
From 20 October 2020:
“Current evidence suggests that the main way the virus spreads is by respiratory droplets among people who are in close contact with each other. Aerosol transmission can occur in specific settings, particularly in indoor, crowded and inadequately ventilated spaces, where infected person(s) spend long periods of time with others, such as restaurants, choir practices, fitness classes, nightclubs, offices and/or places of worship.”
From 23 December 2021:
“Current evidence suggests that the virus spreads mainly between people who are in close contact with each other, for example at a conversational distance … The virus can also spread in poorly ventilated and/or crowded indoor settings, where people tend to spend longer periods of time. This is because aerosols can remain suspended in the air or travel farther than conversational distance (this is often called long-range aerosol or long-range airborne transmission).”
A Cached Belief
I find this Wired article an important exploration of an enormous wrong cached belief in the medical establishment: namely that based on its size, Covid would be transmitted exclusively via droplets (which quickly fall to the ground), rather than aerosols (which hang in the air). This justified a bunch of extremely costly Covid policy decisions and recommendations: like the endless exhortations to disinfect everything and to wash hands all the time. Or the misguided attempt to protect people from Covid by closing public parks and playgrounds, which pushed people to socialize indoors instead.[1]
Finally, here’s a 2006 paper by Lidia Morawska, who features prominently in the article, on droplet transmission:
This potential proved harder to realize than expected.
On Trusting the Experts
This story is one of the lessons from the Covid years which I come back to most often. The screw-up informs how I think about questions of expertise, like to which extent I can trust experts and whether experiences from the Covid pandemic should reduce that trust.[2]
And what does it even mean to “trust the experts”, when there are multiple factions which claim expertise on a topic?
From the article, about a Zoom meeting in April 3, 2020:
So the article obviously takes the side of the aerosol scientists, including calling one “revered”, and calling a WHO expert “rude”. And given that the WHO eventually relented on this issue[3], that makes sense. But an article which takes sides more than a year after the fact doesn’t help us as much to decide which experts to trust in the moment.
That being said, when a big organisation like the WHO makes factual claims with far-reaching economic consequences, and is then very slow to change its mind, and to my knowledge neither apologizes for the mistakes nor fires or even just reprimands anyone responsible, that certainly makes me trust it a lot less.
Conversely, I studied physics, so I can just follow my own tribal instincts and decide to trust the physicists over the doctors.
Maybe it’s easy to decide which experts to trust, after all!
I wonder how a what-if scenario would’ve worked out where everything about Covid stayed the same, except that this cached belief had been corrected before 2020.
Unfortunately I don’t have any great answers here. Experiences like these mostly push me towards more skepticisim and epistemic learned helplessness.
This article in Nature has a timeline of the slooowly evolving WHO statements:
From 9 July 2020:
From 20 October 2020:
From 23 December 2021: