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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

#131

Post by caddemon »

splithalf wrote: post #126
caddemon wrote: post #122

Earlier quoted context omitted.

The RCTs I have seen with basic surgical masks also seem to focus only on protection of the wearer, whereas on a societal level wearing even a shitty mask may be helping to prevent spread by presymptomatic people. I think it is unlikely the positive outcomes in mask wearing communities are purely due to confounders, although of course they probably also play a role.

I suspect mask wearing increases social distancing. That would explain much of the data but satisfy neither political party.

I'm not sure about that honestly. At the extreme there's definitely COVID deniers who followed no precautions, but IME most "normal" people I know felt more comfortable spending time indoors with masks than they would have otherwise. And 6 feet is really not enough spacing in many indoor environments. With things like elevators the other person could be gone and you could still be exposing yourself.

There is also precedence for some of these statistics with Asian countries during the SARS pandemic, and in these places rule following is generally much better.

And with a smaller sample size there are some case studies from restaurant transmission. Staff seem to get infected less frequently than other diners, even though they are in the space for longer. There are a few possible explanations, but the fact that staff don't take their masks off is a pretty compelling one.

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

#132

Post by jwlake »

neither_color wrote: post #45
cr1895 wrote: post #19

Earlier quoted context omitted.

Here’s a nice interactive graphic showing how masks block particles: https://www.nytimes.com/interactive/2020/10/30/science/wear-...

That's a very cool visualization and I wish I'd seen it before. I am curious though as to what makes some viruses have higher R values than others. These masks more effectively stopped influenza and I still don't understand why.

Google cross-protection and competition in respiratory viruses. Lots of pre-2019 literature.

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

#133

Post by awb »

samatman wrote: post #41
awb wrote: post #12

Earlier quoted context omitted.

Years ago my entire family got sick and I was determined not to contract it through distancing and frequent hand washing and sanitizing. It worked until I bent down to tie my toddler’s shoes only to look up and mid-sentence have him cough directly into my open mouth. All it takes is one mistake. Needless to say I got sick shortly after.

I wonder what the result would have been if you immediately gargled with vodka. I've used that successfully in the past to chase colds out of the throat before they get into my nose and lungs.

I’ll try that next time!

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

#134

Post by mattzito »

tgsovlerkhgsel wrote: post #128
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…

What I don't understand... the UK was already doing challenge studies (intentionally infecting consenting volunteers). Why didn't they make one with masks? Really can't be that hard to take a known infected person, sit them on a chair, arrange 100 people around them for a few hours with masks applied in a checkerboard pattern, and observe the results. This is usually out of question for ethical reasons, but they alre…

The challenge studies they’re doing involve infecting people with measure doses of the virus. An infected person may or may not be shedding at that particular moment. Once they’ve established the MED to infect someone, they could potentially do a study with aerosols and masks, but even then, trying to simulate the right airflow and volume of viral particles is probably too difficult to be practical.

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

#135

Post by panarky »

rsj_hn wrote: post #75
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?

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…

> The effectiveness of masks, however, is still under debate

Effective for the mask wearer, or effective for others in the vicinity of the mask wearer?

It's well established that cheap cloth masks and procedure masks don't protect the mask wearer very much.

The rationale for cheap masks is that they drastically reduce the spread of particles from the wearer to everyone else nearby.

If your goal is to protect yourself, wear an N95 or better.

If your goal is to protect a population, and N95s aren't available, then the cheap mask help a lot when people wear them.

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

#136

Post by bellyfullofbac »

Mediterraneo10 wrote: post #124
bellyfullofbac wrote: post #102

Earlier quoted context omitted.

Yeah, it's disappointing to see how I still see people wearing their masks incorrectly, e.g. just over the mouth and not covering their noses. Sometimes I think human beings are advanced, but then I walk into a public toilet and I see evidence how many are still no better than animals. It's a simple technology, urinate into the hole where the water can wash it away and we'll remain hygienic, but a lot of people still…

There are a couple of defensible reasons that people don’t put their mask over their nose outdoors. Firstly, if you wear glasses, then on humid days your glasses can fog up to a degree that you can’t even cross the street safely. Secondly, in some countries the public has chafed against laws requiring outdoor mask wearing in places that are not even remotely crowded. (In my own country, the same scientists advising t…

To elaborate, I saw these people inside a supermarket, where it's probably in their own interest to wear it properly. And no they weren't glasses wearers.

But yes governments just repeating unscientific rules also annoy me, I agree in the empty outdoors masks are most probably unnecessary. (This statement is hedged because hey, I'm not an epidemiologist). They emphasize the "6ft apart" stuff but not the ventilation of indoor places...

And they say outdoor dining is okay, so restaurants put up tents which are poorly ventilated, and hey, the fucking things are outside, that follows the rules, so that means they're safe, right?

I should just join Wonko the Sane outside the asylum...

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

#137

Post by admissionsguy »

nerdponx wrote: post #118
admissionsguy wrote: post #80

Earlier quoted context omitted.

Working down from the conclusion to find the necessary assumptions is the standard approach to COVID-related questions.

This is a valid way to do science. "What assumptions are required to make this conclusion valid?" If the assumptions turn out to be outlandish, then maybe we can't take the conclusion to be true.

In principle, sure, but here, it's just grotesque.

They admit RCTs show masks don't matter, so they put together a few differential equations (which most certainly could be chosen differently to support something else entirely) such that in some domains (virus-limited) masks help a lot, in some (virus-rich) not.

Then they implicitly assume that RCTs didn't show anything because they were done in virus-rich environments and somehow conclude from this dubious claim that "Face masks effectively limit the probability of SARS-CoV-2 transmission".

Am I not reading it correctly?

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

#138

Post by auser1443231 »

omginternets wrote: post #99
joshuaengler wrote: post #74

The VAST majority of mask wearing I have seen in California has been average cloth-covers. I have only seen a handful of people out of thousands actually wearing N95 masks, so perhaps N95 is highly effective at stopping viruses, but I see basically nobody wearing that. Stores, offices, buildings, all are completely fine with you wearing a bandana over your face. There is effectively no point in even mandating mask la…

>The coffee filters people are wearing over their face will do close to nothing I'm not an expert, but I believe this is not quite accurate. As I understand it, even a piece of cloth helps prevent the spread of the virus to others . The mechanism is that the virus exits your nose/mouth in the form of macroscopic droplets that later break down into microscopic droplets a few inches from your face. A bandanna will catc…

It's accurate. A single layer mask made of quilters cotton has been shown to have a filter efficiency of ~9 without gaps[0]. Gaps in all unfitted masks (the type of masks worn by 99% of the citizenry) are thought to reduce efficiency by over 60%, so you're looking at ~9 *.6 = ~5% filter efficiency. That's worthless.

A surgical mask is a little better but not much. There's a reason the FDA, which regulates masks, still maintains that surgical masks are not meant to prevent the spread of aerosols[1], which the CDC has confirmed to be a primary mode of transmission. That's also why, if anyone remembers, you'd see "DOES NOT PREVENT THE SPREAD OF COVID-19" in big bold letters whenever you tried to buy masks on Amazon.

Honestly, anecdotal evidence should be enough. Why do people think that states without strict mask mandates have nearly identical infection rates as those with strict mandates?

Mask mandates don't work. They just don't, and people need to stop playing identity politics with that fact.

[0]: https://pubs.acs.org/doi/10.1021/acsnano.0c03252 [1]: https://www.fda.gov/medical-devices/personal-protective-equi...

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

#139

Post by oasisbob »

chrischattin wrote: post #37
brobdingnagians wrote: post #22

This isn't a study; it is a mathematical model [1]. > Here, we develop a quantitative model of airborne virus exposure that can explain these contrasting results and provide a basis for quantifying the efficacy of face masks. We show that mask efficacy strongly depends on airborne virus abundance. Based on direct measurements of SARS-CoV-2 in air samples and population-level infection probabilities, we find that the…

Yeah, this right here. Masks efficacy for stopping viral transmission has been heavily studied. I could post literally hundreds more examples of statistically significant, RCT'd science showing they have no effect on viral transmission. Wearing masks has never been about the science.

> I could post literally hundreds more examples of statistically significant, RCT'd science showing they have no effect on viral transmission.

Please do. I'm only aware of about a half-dozen controlled trials of mask usage, and they're all low-powered.

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

#140

Post by jonplackett »

rsj_hn wrote: post #75
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?

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.

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