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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

#161

Post by addicted »

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…

Considering that the vast majority of cases of COVID are asymptomatic, it’s pretty apparent that the viral load needed to infect someone enough that they even exhibit symptoms, never mind need to be hospitalized, is not easy to achieve. 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.

And when you combine 30% reductions for both the receiver and the emitter, it gets much higher.

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

#162

Post by nostrebored »

omginternets wrote: post #93
vondur wrote: post #88

I don't know. We had some of the highest mask wearing percentages in the country here in Southern California, yet some of the highest infection rates in the world. Something isn't adding up here. I'm guessing if everyone had N95 masks, we would have seen lower numbers however. I don't think the average cloth masks that people are wearing are very effective.

Could it have to do with population density (perhaps even only in certain areas)? My reasoning is that you could have high transmission among the minority that doesn't wear masks, and that might suffice to make the absolute case-load quite high.

Counterpoint: Miami

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

#163

Post by __blockcipher__ »

panarky wrote: post #135
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…

> 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 yoursel…

Except there is no convincing evidence that they actually do help others, and the whole theoretical mechanism is centered around catching large respiratory droplets which is at odd with the totality of evidence pointing towards aerosol being the dominant mode. I would add if droplet transmission is the dominant mode, which I very much doubt, then masks would still fail in a real-world setting when you look at the fact they make conversational partners stand closer or speak louder, and the massive cross contamination that happens to almost everybody wearing these pieces of cloth over their faces (hands touch mask, mask touches hands, etc)

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

#164

Post by [deleted] »

andreygrehov wrote: post #155
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…

> observational data show that regions or facilities with a higher percentage of the population wearing masks have better control of the coronavirus disease Which is also not entirely true. There are quite a lot of regions (data from worldometer, statista) that have a better control of the virus despite people not giving a crap about face masks. For instance, Florida has 1600 deaths/M vs 3000 deaths/M in New Jersey.…

[deleted]

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

#165

Post by xkcd-sucks »

panarky wrote: post #135
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…

> 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 yoursel…

I wear "n95" masks while sanding drywall, obviously trying to make the fit as good as possible, and still my boogers end up with tons of plaster in them. I would assume these particles to be bigger than any virion.

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

#166

Post by tripletao »

brobdingnagians wrote: post #61
takeda wrote: post #47

Earlier quoted context omitted.

The study about mask being ineffective is about cloth mask. That's why the hospital masks are no longer made of cloth.

That is true; but a large number of people are walking around with cloth masks believing that they are helpful, while that study has shown them to potentially increase risk. It did show "Penetration of cloth masks by particles was almost 97% and medical masks 44%." So that was a positive for medical masks. Though some of the other studies address how those need to be used properly and not re-used. The main point is t…

The Vietnamese study found that cloth masks increased risk compared to medical masks, not compared to no mask. Confusingly, their control group also wore masks, just in fewer situations:

> Hospital wards were randomised to: medical masks, cloth masks or a control group (usual practice, which included mask wearing).

The first paper doesn't say what kind of mask the control participants wore, but a subsequent paper says only 38/458 control participants wore a cloth mask. I think the implication is that the rest wore medical masks, though neither paper ever says explicitly.

https://bmjopen.bmj.com/content/10/9/e042045

That subsequent paper is a subgroup analysis that should be treated with some care, but found comparable performance between medical masks and cloth masks washed in the hospital laundry. That suggests the problem was inadequate hand-washing, not the masks themselves.

There is zero evidence that masks increase incidence of disease compared to no mask. RCTs of mask use in public (e.g., DANMASK-19 and earlier flu studies) suggest that the benefit of the mask to the wearer--excluding the benefit of the mask to others nearby from source control--is less than a 50% reduction in disease, with a 95% confidence interval centered somewhere around 20% but including zero. The RCT evidence says nothing beyond that.

Public health authorities have indeed spoken with unjustified confidence as to the efficacy of masks. You're doing the same thing here in the opposite direction, though. Given the information above, can you correct your comment?

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

#167

Post by chrischattin »

oasisbob wrote: post #139
chrischattin wrote: post #37

Earlier quoted context omitted.

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.

Here's a meta-study of 10 you can peruse...

"In pooled analysis, we found no significant reduction in influenza transmission with the use of face masks (RR 0.78, 95% CI 0.51–1.20; I2 = 30%, p = 0.25)"

https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article

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

#168

Post by userbinator »

anonymousiam wrote: post #35

Here's the manufacturer's (3M) label: WARNING: This respirator helps protect against certain particulate contaminants but does not eliminate exposure to or the risk of contracting any disease or infection. Misuse may result in sickness or death. For proper use, see supervisor, or User Instructions. https://multimedia.3m.com/mws/media/1837275O/3m-9132-healthc...

That's standard legal ass-covering.

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

#169

Post by caddemon »

__blockcipher__ wrote: post #160
caddemon wrote: post #131

Earlier quoted context omitted.

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 pre…

> 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. IMO that’s the least compelling reason. One big one would be the staff having way more contacts and thus higher exposure to the other circulating hCoVs as well as SARS-2 itself. The evidence f…

It is possible for there to be multiple modes of transmission, and there is good evidence to suggest droplet transmission plays a meaningful role in COVID spread. How much it contributes versus airborne transmission may be debatable, but that doesn't mean taking preventative measures against droplet transmission is "dogma". Here is some discussion of evidence for droplet transmission https://jamanetwork.com/journals/jama/fullarticle/2768396

I'm also not sure why you would assume staff have had more contacts. The people that were eating at indoor restaurants in the middle of the pandemic were unlikely the type to be limiting their contacts. Most case studies also checked for antibodies after the fact, not just active COVID testing, so prior immunity would have been detected.

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

#170

Post by fancifalmanima »

andreygrehov wrote: post #155
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…

> observational data show that regions or facilities with a higher percentage of the population wearing masks have better control of the coronavirus disease Which is also not entirely true. There are quite a lot of regions (data from worldometer, statista) that have a better control of the virus despite people not giving a crap about face masks. For instance, Florida has 1600 deaths/M vs 3000 deaths/M in New Jersey.…

https://www.worldometers.info/coronavirus/usa/new-jersey/

https://www.worldometers.info/coronavirus/usa/florida/

It looks like New Jersey was hit early on (when it was also rampant in New York) and Florida got hit later. It could be that hospitals do better at treating it now. Obviously that's speculative. But there are like 30 things I could think of that would make it difficult to make direct comparisons between states. Climate is another one -- Florida is nice all year round, so you can have family/friend gatherings outdoors. I also live in a warm state, and we've just done family/friend stuff outside, even Christmas. At this point we do things indoors when everyone there is vaccinated, and outdoors otherwise. In the case of Florida, turns out all those people that ignored restrictions and went to the beach were something like like 20x less likely to spread it than people spending time indoors. Again... speculative. Point being, you'd have to somehow have the data you need to properly control for a multitude of factors if you wanted to make direct comparisons (including some solid reasoning on what to control for).

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