This pandemic should upend how biologists think about virus transmission—for the better. My greatest regret is having parroted received wisdom early on. I said our @NEJM aerosol stability findings were important for HCW 1/n
But I added that there was "currently no evidence" that everyday people in everyday settings needed to worry about aerosol spread. I publicly changed my tune after the Skagit choir cluster, which I saw—and still see—as strong evidence 2/n https://twitter.com/dylanhmorris/status/1245171019456929792
In my work, I make mechanistic mathematical models of biological systems. Experiments are an important part of science, but so are theory, mechanisms, and models. We can often draw strong inferences from known physics, chemistry, and biology before we even do a new experiment 3/n
And there, there *was* evidence, even before Skagit. People produce small respiratory particles when talking, breathing, and singing. Respiratory virus virions can be found within them. This alone means that we should not rule out aerosol transmission in everyday settings
I didn't know these facts. I suspect many biologists and many doctors didn't. I learned them from @linseymarr and her many excellent colleagues in aerosol science and air quality research 5/n
Once you have that key mechanistic insight, most of the arguments against aerosol spread fall to pieces. My (least) favorite is the "aerosols-means-measles" fallacy: that if a disease is capable of aerosol-driven transmission, it will be extremely transmissible à la measles 6/n
But there are many ways for infectious diseases to differ in transmissibility besides principal route of transmission. People who think flu and SARS-CoV-2 are both mainly transmitted by large, ballistic particles don't expect them to have identical transmissibility! 7/n
And so knowing that aerosols are generated and carry virions should be enough to say that aerosol-driven transmission can happen 8/n
We have a conflict between the fundamental biology of respiratory virus transmission—"inhaling a particle containing a virion can infect you"—and the claim that "virions in aerosols means measles-level transmissibility". 9/n
But given that there are many ways for viruses to vary in transmissibility, I'm going to go for rejecting "aerosols means measles"! 10/n
It was mechanistic thinking that led me to advocate mask wearing early on, and argue that studies cited against mask wearing were either flawed or misinterpreted https://twitter.com/dylanhmorris/status/1242821787387400194
I wish I had done more of my own research into the mechanisms of human aerosol production. Then I could have applied the same thinking to aerosols that I applied to masks. But fortunately @linseymarr and others were around to educate me on the mechanisms. 12/n
Even our cautious statement in our @NEJM article that aerosol transmission of SARS-CoV-2 was "plausible" got us *hammered* by some folks on the aerosols-means-measles side of things. They accused us of sensationalism and scaring people. 13/n
But of course what they heard us saying by "aerosol transmission is plausible" is "measles-like-transmission is plausible". So it's understandable that they saw that as a potentially huge claim 14/n
But this is where the pandemic upending how biologists think about transmission is such a welcome learning opportunity. Aerosols doesn't mean measles. Aerosol-driven transmission may happen for flu, for SARS-CoV-2, for endemic human coronavirus, etc 15/n
So why then is measles measles, chickenpox chickenpox, SARS SARS, and flu flu? Well, let's find out! /end
Actually, not /end. Important coda!

You may be wondering "so if aerosols doesn't mean measles, what *does* it practically mean for me?"
1) Ventilation is key. Outdoors is safer than indoors, and better ventilated indoors is safer than less well ventilated indoors.
2) Masks help. Contrary to popular belief, even cloth masks can filter small (aerosol sized) particles (not perfectly, but don't let the perfect be the enemy of the good!). Conversely, more filtration is always better. If we could get everyone a well-fitted N95, we should!
3) 6 ft of distance from others may not provide sufficient protection if you spend a long time in a poorly ventilated space.
4) 6 ft is better than 3 ft and worse than 9 ft whether you're indoors our out. But increased distance helps more outdoors, thanks to better ventilation

/end for real this time
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