Noah Brier | September 30, 2021

The Paradigm Shift Edition

On cycles, learning, and COVID

Noah here. Last June I wrote about scientific philosopher Thomas Kuhn and his theory of paradigms:

Kuhn said that revolutionary changes, like the one Newton brought, “involve discoveries that cannot be accommodated within the concepts in use before they were made.” He called these revolutionary changes paradigms in his 1968 book The Structure of Scientific Revolutions and explained that they fundamentally shape every aspect of how we think about the world. “Like the transition to Newton’s Laws of motion, they involved not only changes in Laws of nature but also changes in the criteria by which some terms in those laws attached to nature.” 

Science, according to Kuhn, isn’t a linear march forward but rather a cycle where we build up evidence for a scientific theory until it becomes the accepted paradigm, a status it maintains until we spot enough anomalies that it falls over and we start the cycle anew. 

A simplified version of Kuhn’s model from a 1997 HBS Working Paper by Clayton Christensen titled “Competitive Advantage: Whence It Came, and Where It Went”

Why is this interesting?

I have a pretty strong suspicion that over the last year we have started to see some holes in the paradigm of droplet-based viral spread. Last March we were all told in no uncertain terms that COVID came from large droplets and that we needed to clean surfaces, wash hands frequently, and avoid touching our faces to prevent the spread. As long as we stood far enough away, we were assured the large droplets that might come from someone’s nose or mouth would fall to the ground ballistically. COVID, in other words, was not airborne. This, as a great Wired article on the droplet/aerosol debate, has been the paradigm of infectious disease for a very long time.

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 in.

What’s the distinction between a droplet and an aerosol? According to the literature, it’s all about its size. Over 5 microns, or around 1/15th the width of a hair, it’s a droplet, under 5 microns it’s an aerosol. One sinks and the other floats. The problem, as a bunch of experts focused on physics, air, and ventilation have been pointing out, is that the science doesn’t actually work that way. “Reality,” the Wired piece goes on to explain, “is far messier, with particles much larger than 5 microns staying afloat and behaving like aerosols, depending on heat, humidity, and airspeed.” COVID-19, these experts screamed, was almost certainly airborne, which means we need to take precautions like wearing better masks, cleaning the air with filters, and, most critically, moving air in and out as much as possible. Six feet wasn’t going to do the trick if this virus was floating around the room.

Over the last eighteen months, we’ve seen quite a bit of pushback on the aerosol theory of COVID transmission, though thankfully that seems mostly behind us by now. In May, the CDC acknowledged that the main way the virus spreads is through the air: “COVID-19 spreads when an infected person breathes out droplets and very small particles that contain the virus.” (It took the WHO until July.)

All is not lost, though. The upside of this flip-flopping and consternation with the current paradigm is a real possibility to change the way the world deals with respiratory viruses in the future. In May a group of 36 scientists published an article in Science titled, “A paradigm shift to combat indoor respiratory infection” that offered a set of recommendations for how to take what we’ve learned to make the world a safer place moving forward.

The COVID-19 pandemic has revealed how unprepared the world was to respond to it, despite the knowledge gained from past pandemics. A paradigm shift is needed on the scale that occurred when Chadwick’s Sanitary Report in 1842 led the British government to encourage cities to organize clean water supplies and centralized sewage systems. In the 21st century, we need to establish the foundations to ensure that the air in our buildings is clean with a substantially reduced pathogen count, contributing to the building occupants’ health, just as we expect for the water coming out of our taps.

Hopefully, at the very least we will be able to say that all the suffering caused by COVID over the last year-and-a-half led to changes that kept us safe in the future. (NRB)


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Thanks for reading,

Noah (NRB) & Colin (CJN)

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