Thursday 16 April 2020

Zorro me

Hokay! I give up, I'm convinced; masks are good. The controversy has been partly because the opposing sides had been talking about different things. Like the debate about how vultures found their prey - it turned out that both the ayes [👁👁] and the noes <snif><snif> had it correct for different classes of vulture.

With masks, one group of hospital professionals were talking about N95 hazmat respirators which require careful adjusting around the nose and chin to stop incommming particles from getting to your mucous membranes. The other group, including pretty much everybody in Korea, were talking about disposable courtesy masks made of viscose / rayon. These are sometimes called surgical masks because they are used in operating theatres to stop drupples falling from the doctors' nose into the 'working space' below.

N95s are The Biz in the same way as the chain-saw is a great labour-saving device. If you haven't been properly trained in chain-saw care, maintenance, adjustment and usage then you've got a limb-lopper and I'm not talking branches. Getting an N95 on and off without touching your face with contaminated hands requires training and practice. The professionals therefore felt, on the balance of risk, it was better for normal people to not use masks and just stick to the hand-washing.

Surgical masks also do what it sort of says on the tin; they are designed to protect other folks from your spittle rather than saving you from getting a dose. For that to be effective, you need a cultural shift so that [nearly] everybody wears them. By wearing one [my bandito bandanna top L is better than nothing] I'm protecting you and not worrying that I look like an escapee from a John  Ford film. By not wearing one, you are putting me in hazard especially if I've just seen you reaming out your nose with a finger.

But it's not about my assertions; (my don't do as I do, do as I say tbh.)  Show me the data: yer 'tis: a meta-analysis of many studies of the efficacy of masks in helping flatten the curve. It's driven by  Jeremy Howard, an Ozzie working at the Data Science Institute in San Francisco. Here's the formal analysis [not yet peer-reviewed].That's him [R] in the midst of a hilariously terrible video showing how to make a mask out of a t-shirt. Luckily the instructions are simpler than a chain-saw manual and probably make the criterion Why, a child of six could do that.  Here he is with a not-much-better demonstration of how droplets spatter-travel and how a sheet of kitchen paper will stop their gallop. Maybe follow his arguments on twitter.

One thing I like about this solution is that it is super low-tech and achievable without even a sewing machine. The other is that it doesn't require 100% compliance for our community (be that the 700 people who live near Borris Co Carlow or the 7 billion people everywhere). The graph [L] shows that everyone can have a kinda crappy mask and the curve will flatten and/or you can accommodate folks with eczema and anti-vaxxers and folk who are sorted thanks with their tin-foil hat]. R0 is the transfer / infection rate which experts guessimate at 2.4 people infected by each covid-19 positive person. If we-the-people can get R0 below 1.0 then the virus will dry up and blow away.  That's the dark blue top right corner of the graph. You can get over the critical 1.0 line with masks that catch 80% of the outgoing spittle IF you can blag 60% of your neighbours to adopt the new fashion. Or 50% compliant neighbours? Better than nothing, folks!

Trish Greenhalgh, Queen of Crap Detecting [bloboprev], is singing from the same hymn-sheet in the BMJ. Her team point out that a) there have been few proper trials of the efficacy of mask-wearing b) those studies that have been carried out are not uniformly convincing. But, they advocate wearing masks on the Precautionary Principle Effect PPE [no not that PPE]: IF something is easy / cheap to do and it may stop you or your neighbour's grannie getting a fatal dose of Covid-19 THEN what's not to like about doing it?

In an ideal world this social distancing plus will work as one strand of a troika of other measures:
  • Widespread testing
  • Contact tracing of positives
  • Quarantine of affected people
But those require a police state and/or a really biddable, compliant population. Without those active measures we might have to carry on masking for a considerably longer time. But doing a little for a potentially big pay-off seems sensible. Czechia and Slovakia are re-united in making masks compulsory when out and about. Pic credit

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