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.
The next variable in the model here is viral load. It's hugely variable from person to person, and this is honestly a big variable in your chances of picking up COVID in a given situation. We've all heard of "super spreaders" and this is why.
"SARS-CoV-2 viral load
SARS-CoV-2 viral load detected by RT-PCR in nasopharyngeal swabs is widely distributed, ranging from 3 to 10 log10 copies/ml with a median of 6.78 log10 copies per ml [79]. The limited data on viral load in exhaled breath suggests high variability between infected individuals. While not every infector has detectable virus in exhaled breath, those who present detectable virus in breath range between 2-7 log10 copies for 15-60 minutes of expiratory activity [80]–[82]."
"The wide variation in viral load between individuals depends on factors such as age [85], [86], vaccination status [87], [88] and possibly exposure history, and variants of concern [89], [90]. Moreover, the highest mean viral load occurs quickly after symptom onset and at a higher magnitude in individuals with more severe COVID-19 symptoms [85], [91], [92]. The viral shedding episodes have a sharp upswing to reach the peak viral load, followed by a prolonged decay [85], [88]. The duration of viral shedding varies widely and correlates with viral load peak [93]."
