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Face masks effectively limit the probability of SARS-CoV-2 transmission

science.sciencemag.org

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Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#321

Post by makomk »

jonplackett wrote: post #140
rsj_hn wrote: post #75

Earlier quoted context omitted.

Indeed this is the money paragraph: "The effectiveness of masks, however, is still under debate. Compared to N95/FFP2 respirators which have very low particle penetration rates (around ~5%), surgical and similar masks exhibit higher and more variable penetration rates (around ~30-70%) (2, 3). Given the large number of particles emitted upon respiration and especially upon sneezing or coughing (4), the number of respi…

I really don’t get why this is still considered a conundrum Lots of places have R hovering around 1. If it goes to 1.1 everything goes to shit, if it drops to 0.9. Everything will be fine. So even if masks reduce spread by a tiny amount, even 10% better. That could easily swing you below 1 and save the day.

The trouble is that this doesn't actually work. By using R this way you're assuming a model where every person is equally likely to spread the infection to every other person in the population, which is easy to calculate but what actually happens. In reality people can only spread the virus to those they're in contact with, and (say) a supermarket employee can spread the virus to more people than someone working from home and not socializing due to social distancing rules. Not only that, there are clusters of people who are all likely to spread the virus to more people or to less people when infected, such as workers in food manufacturing, people in dense urban areas vs less dense areas, etc...

So what actually happens in reality is that if R is hovering around 1, there are going to be some places where it's actually above 1 and cases are growing exponentially, and some where it's below 1 and they're shrinking exponentially. The end result of this is that places where R is actually below 1 make up an exponentially shrinking proportion of all cases, and as this happens it causes the overall measurement of R to go back above 1.

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#322

Post by dtech »

himinlomax wrote: post #286
hermitcrab wrote: post #263

Earlier quoted context omitted.

If you wore a mask in public in the UK before COVID, you would have got some very strange looks. They might have thought you were a criminal trying to hide your face. It seems fairly normal now though.

It's worse than that, you'd probably had been harassed by the police, or just simply arrested.

Bullshit, while rare, more than a few people wore them in train stations or airports.

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#323

Post by jvvw »

function_seven wrote: post #113
rsj_hn wrote: post #75

Earlier quoted context omitted.

Indeed this is the money paragraph: "The effectiveness of masks, however, is still under debate. Compared to N95/FFP2 respirators which have very low particle penetration rates (around ~5%), surgical and similar masks exhibit higher and more variable penetration rates (around ~30-70%) (2, 3). Given the large number of particles emitted upon respiration and especially upon sneezing or coughing (4), the number of respi…

> On the other hand, "observational data show that regions or facilities with a higher percentage of the population wearing masks have better control of the coronavirus disease 2019 (COVID-19) (7–9)." So how to explain these contrasting results and apparent inconsistencies? My hypothesis regarding surgical mask prevalence and how it correlates with better virus control: People who wear masks--however effective they m…

There is also a question as to the extent to which the current rules send a signal to be careful or not. Anecdotally and highly subjectively, I felt like when schools were closed here in January, everybody started being more careful generally - as though closing schools went a strong message that it was time to be cautious again, more than just announcements about virus rates would have done.

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#324

Post by BurnGpuBurn »

tgsovlerkhgsel wrote: post #39

This entire study seems to be centered around a theoretical, mathematical model, and I didn't see any attempt to actually validate that model. Basically, the authors seem to assume that the virus behaves according to their formulas, and show that under their assumptions, face masks work, but don't actually prove that their assumptions match reality - or did I miss something?

You are correct, although I wouldn't call this a study. It's a science paper, yes, but it doesn't contain any new data that has been studied, just some fancy formulas and graphs and conjecture by a couple of people with a science degree.

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#325

Post by makomk »

simpleguitar wrote: post #179
nimish wrote: post #144

Earlier quoted context omitted.

Nope. It's circular. We need actual tests in the wild, not models.

During an interview with some of the doctors sent into Wuhan in their wave, they claimed none of the 10 thousand or so doctors sent in became infected. They used strict PPE protocol, including N95 masks. Given what we know about the covid transmission now, it was absolutely the N95s that prevented these doctors from getting infected.

If I remember rightly, what they actually claimed is that none of the doctors sent in were infected in the hospitals. That is, there were doctors sent to Wuhan who caught Covid, but the Chinese government blamed it on them becoming infected from contact with people outside of their work.

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#326

Post by chimprich »

petertodd wrote: post #62
matz1 wrote: post #54

Earlier quoted context omitted.

The problem is wearing mask is annoying and uncomfortable. If I have to choose, I'll choose the increased risk of covid all the time rather than wearing mask.

A big part of why they are annoying and uncomfortable is the lack of one-way valves to make it easier to breath in them. In industry, when you actually need to wear a mask/respirator, they almost always have valves. Unfortunately, we got stuck on the "wear masks to protect others" narrative, and people who actually were at risk were prevented from wearing much more effective, much more comfortable, masks that would a…

> Unfortunately, we got stuck on the "wear masks to protect others" narrative

Why is that "unfortunate"? Surely discomfort is less important than actually protecting life?

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#327

Post by chimprich »

maxerickson wrote: post #320
chimprich wrote: post #315

Earlier quoted context omitted.

That doesn't make a lot of sense. Higher initial load means higher severity but a lower initial load doesn't mean lower severity?

A lower initial load doesn't guarantee a low severity because the timing of the immune response is such a big factor (due to the large reproduction exponent). As such, it’s likely even a 30% reduction (which is on the lower end of the range) in the viral load inhaled by someone could drastically reduce the chance of symptomatic COVID. is vague enough to not be an over statement, but it probably isn't easy to find muc…

A lower initial load leading to less severe disease makes intuitive sense (less opportunity for the infection to outpace the immune response) and whilst not proved, a lot of virology experts think it's plausible.

There is at least some evidence for it, e.g. a military base study that found less severe disease cases once masks started being worn.

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#328

Post by chimprich »

asabjorn wrote: post #253
sschueller wrote: post #17

N95/FFP2 seem to be very effective. I wish the media and government would have spent more time in educating people in things like how N95 masks work and that it isn't like a coffee filter. Even thought the pores are larger than a virus the masks are statically charged causes smaller things to get trapped. Many people don't know this but probably had an interaction with static electricity sometime in school and would…

> N95/FFP2 seem to be very effective. Why does then the states with the highest mask use (CA, NYC) have much higher covid positive rates than states with some of the lowest mask use (Florida, NYC)? > Education is key to understanding. You can't reach everyone most. N95 masks improperly used will hold covid for 24hrs and spread them by the incessant touching most people do of their masks before they touch other things…

> Why does then the states with the highest mask use (CA, NYC) have much higher covid positive rates than states with some of the lowest mask use (Florida, NYC)?

Even if that was true, places that were hit hardest by the pandemic tended to impose the most severe restrictions.

It's like finding that crash barriers are installed on roads with the highest accident rate and asking whether crash barriers are useless.

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#329

Post by beagle3 »

La1n wrote: post #316
beagle3 wrote: post #265

Earlier quoted context omitted.

Unless you have a valve, and hardly breath at all, exhaling pushes the N95 away from your face enough to let some unfiltered air in. There’s a similar (though smaller) effect with the thin paper valves, but regardless of how good the fit is, you need a much better valve than that to actually filter all air through the fabric.

Are there N95's without a valve? Cause all I've owned before the pandemic had a valve.

Yes.

I’ve had both with and without valves since 2015. Would never buy one without a valve again if I can find one with a valve (in the last year at some times could only find valveless)

Fwiw, in Israel it was illegal to use a valved mask without covering the valve with cloth/paper/surgical mask. The official statement was that the pressure out of the valve disperses virions much farther, and is thus more dangerous to people around you if you are presymptomatic than having no mask at all.

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#330

Post by mhb »

admax88q wrote: post #212
mhb wrote: post #97

Earlier quoted context omitted.

3M 8210s are US $26 for 20 now. $1.30 per mask seems pretty reasonable to me, but I've never bought them in industrial quantities so don't have that anchor. I've worn N95s for hours (actually P95s which have a nicer seal) and I agree that they're less comfortable than less effective alternatives. But it is a bit curious that people are concerned enough to be wearing their homemade mask alone in a car or walking outsi…

I wear mine alone in the car or on the sidewalk frequently. Not because I'm "afraid" but because I'm too lazy to take it on and off between every stop I'm going to make. This attitude that people are wearing masks alone because they're afraid and/or stupid is toxic.

Grant me the steel man. What's the mental model of the people wearing them outside on a walk in the woods or on a beach? Not the inconvenience of taking them off between stops at the bank and the drug store.
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