Do masks reduce fatality of #COVID19 due to lower dose?
I've heard this theory a couple times (see below) and so it's worth addressing likelihood of it head on.
Short thread.
I've heard this theory a couple times (see below) and so it's worth addressing likelihood of it head on.
Short thread.
Basic idea for many pathogens: if you infect the host with larger dose you increase chance of infection, & *sometimes* more severe disease. Mechanism: if pathogen grows to high loads before immune system ramps up, disease severity can be higher.
Higher dose=head start for virus!
Higher dose=head start for virus!
Idea w/ masks would be that they might stop big droplets w/ more virus but not smaller droplets so people that get infected do so w/ lower doses. Seems plausible in some settings but there's a flaw with it being an explanation for population patterns...
A very large fraction of all transmission is within households, and most people aren't wearing masks in households. Same for bars, and communal housing and many jails and ...
You get the point. So what could explain apparently different fatality of COVID in anecdotes mentioned?
You get the point. So what could explain apparently different fatality of COVID in anecdotes mentioned?
Most obvious possibilities are age & pre-existing conditions (). Any analysis that doesn't first address these factors is not worth paying attention to. In general, need actual proper analysis not quick eyeball comparison. 
Cruise ship example given in top tweet mixes raw data and analysis. Raw data on fraction asymptomatic for Princess cruise ship is not that different from other boat, but analysis that examines time of testing changes results substantially.
So, do I hope that masks reduce dose of virus that is transmitted and that this results in light infection that is mild and yet provides same immunity? Absolutely!
But am I confident that this is a real factor influencing COVID-fatality in many people. Absolutely not.
But am I confident that this is a real factor influencing COVID-fatality in many people. Absolutely not.
Need careful analysis of actual detailed data before this is offered as real explanation for any apparent pattern.
But plenty of other reasons to wear a mask!
My new motto:
Meet outside, give space, and wear a mask!
But plenty of other reasons to wear a mask!
My new motto:
Meet outside, give space, and wear a mask!
