Friday, 17 September 2021


Flowchart here. Pretty funny

Via Althouse blogpost

I’m not really anti mask, in that I’ll wear a mask where it’s mandated and sensible. But I kind of am as well, since there seems to be a belief in mask effectiveness that’s largely untethered from reliable data. 
Early in this pandemic, in January 2020, I posted something about masks based on our experience during SARS in 2002 and on the then available data. 
[Looking back at it now, how simpler were those times! When posting something about masking didn't immediately slot you into one tribe or another!]
In my post I linked to "What doctors say about wearing masks" from 29 Jan 2020:
By contrast [to N95 respirators], surgical masks — those cheap, disposable, gauzy masks that often come in blue or green — are less uncomfortable. But Schaffner says the scientific evidence that "there might be a benefit for people in the community wearing [surgical] face masks is very, very meager. The general sense is perhaps, but they're certainly not an absolute protection." In other words, they do provide some benefit but they're far from foolproof.
All the evidence since then suggests that that remains pretty much the same. Masks help a bit, but not a lot; N95 are far more help, but are hard to wear and need training to fit properly; surgical masks are of some use; cloth masks basically useless. But I’m guessing — guessing, mind, no science here! — that when officials and health bureaucrats call for masking, they’re imagining (now I’m mind reading)  that masks are a kind of “do or die”. That if you don’t mask you’re at huge risk to yourself and others; if you do mask you’re stopping the virus in its tracks.
Not so quick...
A recent Yale university study, the first large scale randomised study of the effect of masks on spread of Covid, shows that masks do have an effect (it would be surprising indeed if there were no effect), but relatively small even for surgical masks, and close to zero for cloth masks. 
With a p=0.54 the results for cloth masks are not
statistically  significant
Even for the surgical masks the effects for <50yo were not statistically significant:
Moreover, some of the effects of mask wearing may well have been because of increased "social distancing" amongst the intervention group, as the Yale study authors themselves acknowledge. 
Of course, it's also possible to make the case that, extrapolating, the reduction in Covid spread by masking may be greater than the study suggests, as in a twitter exchange by one of the authors, here.
Still: we could always have worn masks to halt the spread of viruses that cause pneumonia, which kills 4-5 million per year. But we didn't do that. Are we going to wear masks as long as we have any Covid in the world, because it saves lives? Other things that save you from Covid: 1. Being slim 2. Being young 3. Being vaccinated.
ADDED: Some other thoughts on the Yale Study:
  • Distancing increased in the intervention group and is part of the reason for the reduction of seroprevalence for that group
  • It's Bangladesh, where the rate of Obesity is low. We know -- or believe we know -- that obesity is a driver of Covid mortality (though some think only a small driver). I don't know whether that might affect the results.
ADDED: One thing I learnt from perusing the amusing flow chart above: Vegans are not getting vaccinated (for various reasons, some around the ethics of animal testing)