3 ms·

Effectiveness doesn't just mean "can this mask trap particles?" -- because it's clear that FFP3 masks can do this. Effectiveness also means "In a particular sit

by DanBC 5y ago

Effectiveness doesn't just mean "can this mask trap particles?" -- because it's clear that FFP3 masks can do this. Effectiveness also means "In a particular situation with a thousand people, how many if them will be infected if none of them wear a mask, vs if all of them wear a mask?" Healthcare professionals have to shave facial hair; they use good quality masks that are tested for conformity; they have sessions where their masks are fitted for them; they have training about how to put on, take off, and wear the mask; they have support to help them put on PPE; and they use the mask as part of a bundle of PPE that includes gowns, gloves, hand-sanitising, and eye protection. In a healthcare situation we see that this package of measures does reduce infection. (And then we struggle to understand what's doing what because it's all a big confounded mess) But for the public, going about day to day activity, it was really hard to see that masks would do much good. And it's hard to do that even today: people in this thread are saying that it's obvious cloth masks do nothing but p95s are super effective. No-one can post any good quality evidence for that. All we get a some pretty rough studies that are trying to disentangle a bunch of measures to see which had most effect.

woofie11 5y ago
What we know is that: * Cloth masks reduce viral loads by somewhere around 30-70%. * High-quality masks reduce them by e.g. 70-95% depending on how they're fitted. * We know risk of infection (and severity) is related to viral load, but we don't quite know how. * We have a lot of well-documented evidence from Asia about reduced infections when high-quality masks are used consistently (e.g. buses in China, hospitals in Singapore, etc.). * We know masks significantly reduce R0, but we don't know by how much; error bars are huge, and dependent on a slew of other variables. The key difference between public health settings and hospital settings is opportunities to be infected. As a doctor, I might have 10 opportunities per day, and if I don't have properly-fitted PPE one of those times, and I'm susceptible, I'll catch COVID19. This means half-measures do very little. In a public health setting, it's a numbers game: * Personal: If I have 1 opportunity per 2 weeks to be infected, and I reduce odds by 50%, I'm half as likely to catch COVID personally. * Public health: If I reduce infection odds by 50%, R0 is cut in half. That's huge. Our exponent is very different. So cloth masks are definitely worth the $2, but won't stop you from catching COVID if you take other risks. If everyone wore N95 or even surgical or nanofiber masks, COVID would probably be gone pretty quickly.

by DanBC 5y ago

woofie11 5y ago

What we know is that: * Cloth masks reduce viral loads by somewhere around 30-70%. * High-quality masks reduce them by e.g. 70-95% depending on how they're fitted. * We know risk of infection (and severity) is related to viral load, but we don't quite know how. * We have a lot of well-documented evidence from Asia about reduced infections when high-quality masks are used consistently (e.g. buses in China, hospitals in Singapore, etc.). * We know masks significantly reduce R0, but we don't know by how much; error bars are huge, and dependent on a slew of other variables. The key difference between public health settings and hospital settings is opportunities to be infected. As a doctor, I might have 10 opportunities per day, and if I don't have properly-fitted PPE one of those times, and I'm susceptible, I'll catch COVID19. This means half-measures do very little. In a public health setting, it's a numbers game: * Personal: If I have 1 opportunity per 2 weeks to be infected, and I reduce odds by 50%, I'm half as likely to catch COVID personally. * Public health: If I reduce infection odds by 50%, R0 is cut in half. That's huge. Our exponent is very different. So cloth masks are definitely worth the $2, but won't stop you from catching COVID if you take other risks. If everyone wore N95 or even surgical or nanofiber masks, COVID would probably be gone pretty quickly.