Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

science.sciencemag.org

Post reply on HN
Print view View original

311–320 of 387 posts

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

#311

Post by lixtra »

apatters wrote: post #300
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?

My thinking has always been that of all the possible interventions to reduce viral spread, something like making people wear masks while grocery shopping has almost no negative side effects. Whereas closing the grocery store altogether has major negative side effects, like lost jobs and people not being able to buy groceries. So I think the evidential bar for requiring masks should be pretty low (unless it is a speci…

If masks turn out to be ineffective, the cost of having them recommended is reduced reputation and authority.

Would you take security advice from Bruce Schneier after he proposed you to cover your keyboard in snakeoil because it might protect against computer viruses (and if not, there is not much damage)?

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

#312

Post by chimprich »

xkcd-sucks wrote: post #165
panarky wrote: post #135

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…

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.

> I would assume these particles to be bigger than any virion.

The masks aren't expected to stop individual virus particles. They are supposed to catch salivary droplets containing the virus.

These are probably bigger than particles of drywall dust.

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

#313

Post by johbjo »

dragonwriter wrote: post #256
asabjorn wrote: post #245

Earlier quoted context omitted.

> The rationale for cheap masks is that they drastically reduce the spread of particles from the wearer to everyone else nearby. If so, why does states with the highest mask use (CA, NYC) have much higher covid rates than states with some of the lowest mask use (Florida, Texas)?

> If so, why does states with the highest mask use (CA, NYC) have much higher covid rates than states with some of the lowest mask use (Florida, Texas)? They...don’t (leaving out NYC because the other three things are large, diverse states and NYC is a single large city): California 3.7M cumulative cases & 1,336 case/day current 7-day average vs. 39.5M population Florida 2.3M cumulative cases & 3,007 case/day 7-day a…

Also consider age distribution/population density in areas you compare.

Death rate is exponential in age, so small differences in age distribution gives big differences in relative deaths.

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

#314

Post by makomk »

astrange wrote: post #297
nradov wrote: post #238

Earlier quoted context omitted.

How can a model be convincing if it hasn't been extensively tested in the real world?

The model of wearing masks has been extensively tested in Asia. Meanwhile US doctors were telling me that putting on a mask would actually cause you to get infected faster because you'd do it wrong. (Then the CDC announced mask orders the next day and they mumbled something about new evidence to me.) And we can see who's done better in the last year.

It's looking more and more like a whole bunch of Asian countries just got lucky. Singapore, Taiwan and Vietnam have all currently got uncontrolled community spread again (possibly China too), and whilst the Taiwan outbreak could maybe be blamed on them getting sloppy Singapore has been aggressively enforcing mask wearing the whole time.

There was already good reason to suspect this was the case over a year ago too. The early outbreaks mostly seemed to be a gradient emanating outwards from Italy, with genetic testing suggesting that even the US had done reasonably well at halting spread from China and its big outbreaks came from Europe; Asia is obviously a long way from Italy and it was suspicious that a bunch of countries that in reality had widely varying policies on things like masks, testing, etc showed such similar results. Including countries like Australia and New Zealand that were more or less western in terms of culture but were geographically close to the rest.

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

#315

Post by chimprich »

maxerickson wrote: post #186
addicted wrote: post #161

Earlier quoted context omitted.

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 w…

That's not how infections work though. A high initial load can cause the infection to peak higher (because more replication occurs before the immune response), but a lower initial load doesn't necessarily lead to a low peak infection (because replication is exponential with a large exponent).

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

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

#316

Post by La1n »

beagle3 wrote: post #265
simpleguitar wrote: post #177

Earlier quoted context omitted.

A properly fit N95 should block out all dust. If you are getting plaster in your nose, try different types of masks (folding), or a half-face respirator. One of the justification for not advising N95s to the public was the fact that most people don't know how to properly wear one. As if they couldn't be trained in a few weeks, or duration of the pandemic. Also, N95s filter out particles smaller than .3 microns (the 9…

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.

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

#317

Post by dctoedt »

poutine wrote: post #46
neither_color wrote: post #28

Earlier quoted context omitted.

Anecdotally I haven't had a cold in years. I work out 4 days a week and while I wouldn't call it a strict diet I have an upper limit calorie "budget" that I never exceed. While it's certainly possible that masks helped some people avoid all airborne transmissions last year, lots of people were also able to exercise more and make better food choices without the rush of breakfast and lunch commutes.

Get kids. They are plague carriers.

My dad used to refer to day care as "your friendly local disease exchange," because he and my mom would get sick whenever they visited grandchildren.

And a former colleague, then childless, called them "petrie dishes."

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

#318

Post by chimprich »

lixtra wrote: post #311
apatters wrote: post #300

Earlier quoted context omitted.

My thinking has always been that of all the possible interventions to reduce viral spread, something like making people wear masks while grocery shopping has almost no negative side effects. Whereas closing the grocery store altogether has major negative side effects, like lost jobs and people not being able to buy groceries. So I think the evidential bar for requiring masks should be pretty low (unless it is a speci…

If masks turn out to be ineffective, the cost of having them recommended is reduced reputation and authority. Would you take security advice from Bruce Schneier after he proposed you to cover your keyboard in snakeoil because it might protect against computer viruses (and if not, there is not much damage)?

That's an absurd comparison.

Regardless of how well they work in practice, there's a clear theoretical reason why masks could/should work: they catch salivary droplets containing the virus.

Covering your keyboard in oil is not even theoretically going to affect your computer's susceptibility to computer viruses.

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

#319

Post by La1n »

nimish wrote: post #274
simpleguitar wrote: post #243

Earlier quoted context omitted.

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.

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

Lots pharma trials are against current best standard of care and not placebo. Placebo trials are never done in cases where effective therapy is available.

https://www.cancer.net/research-and-advocacy/clinical-trials...

>A: Placebo-controlled trials are never appropriate when a highly effective or potentially curative therapy is available for a patient. An exception is unless the trial allows the patient to receive the new treatment/placebo in addition to the potentially curative therapy. For example, let’s say that a promising new treatment is in development for advanced testicular cancer, a disease that is curable in many cases with the use of chemotherapy. It would not be appropriate for a clinical trial to randomize patients between the new treatment and placebo because potentially curative chemotherapy already exists. However, it might be appropriate to randomize between standard chemotherapy plus the new drug or standard chemotherapy plus placebo because in both cases, patients will receive the standard, potentially curative treatment.

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

#320

Post by maxerickson »

chimprich wrote: post #315
maxerickson wrote: post #186

Earlier quoted context omitted.

That's not how infections work though. A high initial load can cause the infection to peak higher (because more replication occurs before the immune response), but a lower initial load doesn't necessarily lead to a low peak infection (because replication is exponential with a large exponent).

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 much in the way of actual support for it either.

Post reply on HN