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. Six feet wasn’t going to do the trick if this virus was floating around the room. “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. 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. Over 5 microns, or around 1/15th the width of a hair, it’s a droplet, under 5 microns it’s an aerosol. What’s the distinction between a droplet and an aerosol? According to the literature, it’s all about its size. They can spread when contagious people simply breathe in. 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. Only a few diseases were thought to break this droplet rule. If these droplets alight on a nose or mouth (or on a hand that then touches the face), they can cause an infection. This, as a great Wired article on the droplet/aerosol debate, has been the paradigm of infectious disease for a very long time.Īccording 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. 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. 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. 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. 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”
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