Big thank you to @EricCarroll for pointing out this new WHO document on SARS-CoV-2 transmission.
This document is pretty complex, in-depth, dense, and I still expect it to evolve as we learn along the way. They have some of the correct people to be working on this, for once. Hello Lidia Morawska signing off on it at the beginning of the forward.
First, a tldr. If you don't care about how it came to be, or the science, and just want to know the outcome, here it is:
https://partnersplatform.who.int/tools/aria
Go to the calculator, enter your data, and come out with a probability of infection in a given situation along with the number of expected secondary infections from that interaction.
Here's the document itself if you want to follow along:
https://iris.who.int/bitstream/handle/10665/376346/9789240090576-eng.pdf?sequence=1&isAllowed=y
Disclaimer - This is evolving science.
I'm going to split this up in a thread, because I took a lot of notes of what stood out to me on a first read, and I hope to come back to it, and use it as a general reference moving forward.
Next up is a brief discussion of outward control, ie. if you're infectious and you're wearing a mask. I want to reiterate if I haven't made it clear here, these are not the entirety of each section. These are the parts that stood out to me as things I've wondered about, or seen other people asking about, or even just science I thought was cool. If you want to read more on any of this, it's in the document and references.
"Source control (outward)
Throughout the pandemic, the use of well fitting masks to cover the mouth and nose have been widely applied as a source control measure to reduce the emission of respiratory particles and thereby reduce the potential emission of infectious particles from infected people. Studies have supported that wearing a mask to protect others from potentially infectious particles is a highly effective infection control measure to limit the spread of COVID-19 [95], [96]. Well fitting masks provide a physical barrier to the emission of both large and small respiratory particles [97]–[99], and depending on the virus type, are also effective in reducing exhaled infectious particles [71], [84].
Both medical masks and respirators, even without fit-testing, can reduce the outward particle emission rates by 74% and 90% on average during speaking and coughing, respectively, compared to wearing no mask, corroborating their effectiveness at reducing outward emission [97]. In contrast, shedding of non-expiratory micron-scale particles from friable cellulosic fibres in homemade cotton-fabric masks may confound explicit determination of their efficacy at reducing respiratory particle emission [97]."
