Live data from Hacker News

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

science.sciencemag.org

271–280 of 387 posts

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

#271

Earlier quoted context omitted.

I suspect that in locations with a higher prevalence of masking the population is generally more vigilant: more hand washing, more social distance, stay at home when ill, avoid obviously ill people, and so on. May be a case of correlation, not causation. It would be interesting to have a trial where everyone was wearing N95s, but we're not likely to see that.

> I suspect that in locations with a higher prevalence of masking the population is generally more vigilant: more hand washing, more social distance, stay at home when ill, avoid obviously ill people, and so on. May be a case of correlation, not causation. The states with the highest mask use (NYC, CA) has some of the highest covid positive rates, so the data does not seem to back up your assertion.

You seem to be repeating this in several comments, but that's just not true. CA's total per-capita case counts and recent new-case rate is lower than, say, both Texas and Florida.

NYC is not a state, so you can't directly compare it.

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

#272
post #149

We know masks work for infection control which is why they are used in hospitals and also in clean room style manufacturing.

Bacteria and viruses behave differently. It’s possible, even likely, that a measure against one will be ineffective against the other.

In an attempt to fights a specific virus, namely sarscov2 - no, we don’t know that masks work. The cdc numbers I saw talk about 2% reduction in vivo.

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

#273

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)?

They don't. Stop spreading misinformation. (Also I love that in this repeat of your misinformation, you accidentally typed "NYC" where you meant to say "Texas". And it would behoove you to learn the difference between a city and a state.)

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

#274
post #226

Earlier quoted context omitted.

Then run a proper randomized controlled trial with comparisons to cloth and surgical masks so we have actual data, not 10000 anecdotes. This was the biggest event of the last 50 years, we can throw a few billion at a real trial.

One problem--ethics. Can't knowingly give humans less protection. It's not a money problem.

That is what you are testing!

Equipoise demands you don't assume one outcome.

Otherwise every single pharmaceutical trial would be impossible since "we can't knowingly give humans a placebo"

If the effect is large and significant we will see it quickly and can halt asap.

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

#275
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…

"proxy for how serious the wearer takes Covid as a threat." I would suggest that this now law in some countries and that would be the reason for wearing facemasks.

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

#276
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 study also focuses on influenza which does not transmit quite the same way as COVID. A bunch of these links were the same thing being shared in the early days of COVID by doctors claiming that masks did not work. Obviously most healthcare organizations have changed their recommendations in light of new evidence specific to this pandemic.

There doesn’t seem to be any evidence specific to this pandemic that masks work. The CDC study released recently puts it at 2% or so. And there was no new evidence in March that caused the reversal from “masks don’t work” to “you must mask up” to “two masks are better”.

Obviously there was a reason for them to change their recommendations, but it is not evidence, and might not even be health related - I know someone who was involved with a recommendation in a national organization, and a big part of it was “instilling a feeling of pandemic”.

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

#277

Earlier quoted context omitted.

> 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 fac…

People touch their faces all the time, mask or not. And some non-physical effects of masks may be useful. If nothing else, fumbling around with masks is repeated reminder for all other measures.

It may feel silly to wear a mask if you belief that this is the only effect. But you cannot deny that it is a causal effect, e.g. it would not happen without wearing the masks.

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

#278

Earlier quoted context omitted.

I don't understand this myth about Florida. It has fared very badly in the pandemic. You're three times as likely to have died in Florida from COVID, as opposed to in Canada. It sits in the middle of the States, in terms of death rates, which overall have been among the worst in the world. Compare your example to an area where people really take masking serious, such as Hong Kong, and then maybe you'll have a valid c…

>Compare your example to an area where people really take masking serious, such as Hong Kong, and then maybe you'll have a valid comparison. It's not fair to compare the US/Canada with East Asian countries like Hong Kong because the biggest contributor to covid fatality rates apart from population age is obesity rates, which are way lower in East Asia.

I haven't clue about statics so it's likely this is wrong but a quick graph of COVID deaths per million vs obesity rate for each country doesn't look like there is any correlation.

https://jsgist.org/?src=7b456a001284587cb90c7693ac0e6f3b

Also, if age is the #1 factor then Japan should have the worst covid as they have the most old people per capita but they don't. They also haven't locked down but they have worn masks. (not saying masks were why covid is so low here). Yes they are having a spike now. It's still tiny (1/20th) other countries with comparable populations sizes.

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

#279
Obligatory story on Manchurian plague epidemic regarding how surgical mask come to be a standard requirement during the treatment of any airborne disease [1][2].

Mind you that the original surgical mask was not invented for surgery, it was invented for the treatment of patients with airborne virus. Heck, every.single.time you meets someone who are skeptical about the effectiveness of the mask in mitigating the airborne virus transmission, just send them this story [1][2].

It also interesting to note that the inventor of the surgical mask Dr. Wu, (the doctor mentioned in the article) is not even the resident of Imperial China at the time, even though he is the first Chinese medical doctor trained and graduated from the University of Cambridge. The last Empire of China or Qing dynasty who was originally come from Manchuria, had to hire the best medical doctor that they can find in order the save the citizens native of Manchuria, from the raging epidemic. Dr. Wu has come very close to get the Noble price in medicine back in 1935 due to his novel surgical mask invention.

[1]https://insightplus.mja.com.au/2020/15/dr-wu-lien-teh-hero-o...

[2]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4291938/

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

#280
post #236
post #153

Earlier quoted context omitted.

"Some people with swine flu travelled on a plane from New York to China, and many fellow passengers got infected. Some researchers looked at whether passengers who wore masks throughout the flight stayed healthier. The answer was very much yes. They were able to track down 9 people who got sick on the flight and 32 who didn’t. 0% of the sick passengers wore masks, compared to 47% of the healthy passengers. Another wa…

That is not “very much yes”, that is “an anecdote suggests yes”. The statistical illiteracy here is astounding from professional scientists. ”0% of ths sick passengers wore masks, compared to 47% of the healthy passengers. Another way to look at that is that 0% of the mask wearers got sick, but 35% of non-wearers did” And another way to look at it is that 65% of non-wearers didn’t get sick. The group of sick people i…

Error bars would be nice. They're MIA in large swathes of COVID related research. I've read a lot of COVID papers in the past year and this paper is typical of the field. Things you should expect to see when reading epidemiology literature:

1. Statistical uncertainty is normally ignored. They can and will tell politicians to adopt major policy changes on the back of a single dataset with 20 people in it. In the rare cases when they bother to include error bars at all they are usually so wide as to be useless. In many other fields researchers debate P-hacking and what threshold of certainty should count as a significant finding. Many people observe that the standard of P=0.05 in e.g. psychology is too high because it means 1 in 20 studies will result significant-but-untrue findings by chance alone. Compared to those debates epidemiology is in the stone age: any claim that can be read into any data is considered significant.

2. Rampant confusion between models and reality. The top rated comment on this thread observes that the paper doesn't seem to test its model predictions against reality yet makes factual claims about the world. No surprises there; public health papers do that all the time. No-one except out-of-field skeptics actually judge epidemiological models by their predictive power. Epidemiologists admit this problem exists, but public health has become so corrupt that they argue being able to correctly predict things is not a fair way to judge a public health model[1]. Obviously they insist governments should still implement whatever policies the models say are required. It's hard to get more unscientific than culturally rejecting the idea that science is about predicting the natural world, but multiple published papers in this field have argued exactly that. A common trick is "validating" a model against other models [2].

3. Inability to do maths. Setting up a model with reasonable assumptions is one thing but do they actually solve the equations correctly? The Ferguson model from Imperial College, which we're widely assured is one of the world's top teams of epidemiologists, was written in C and filled with race conditions/out of bounds reads that caused their model to totally change its predictions due to timing differences in thread scheduling, different CPUs/compilers etc. These differences were large, e.g. a difference of 80,000 deaths predicted by May for the UK [3]. Nobody in the academic hierarchy saw any problem with this and worse, some researchers argued that such errors didn't matter because they just ran it a bunch of times and averaged the results. This is confusing the act of predicting the behaviour of the world with the act of measuring it, see point (2).

4. Major logic errors. Assuming correlation implies causation is totally normal. Other fields use sophisticated approaches to try and control for confounding variables, epidemiology doesn't. Circular logic is a lot more common than normal, for some reason.

None of these problems stop papers being published by supposedly reputable institutions in supposedly reputable journals. After reading or scan-reading about 50 epidemiology papers, including some older papers from 10 years ago, I concluded that not a single thing from this field can be trusted. The problems aren't specific to COVID, they're cultural and have been around a long time. Life is too short to examine literally every paper making every claim but if you take a sample and nearly all of them contain basic errors or what is clearly actual fraud, then it seems fair to conclude the field has no real standards.

[1] "few models in healthcare could ever be validated for predictive use. This, however, does not disqualify such models from being used as aids to decision making ... Philips et al state that since a decision-analytic model is an aid to decision making at a particular point in time, there is no empirical test of predictive validity. From a similar premise, Sculpher et al argue that prediction is not an appropriate test of validity for such model" https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3001435/

[2] https://github.com/ptti/ptti/blob/master/README.md

[3] https://github.com/mrc-ide/covid-sim/issues/116 https://github.com/mrc-ide/covid-sim/issues/30 https://github.com/mrc-ide/covid-sim/commit/581ca0d8a12cddbd... https://github.com/mrc-ide/covid-sim/commit/3d4e9a4ee633764c...

Post reply on HN