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There are studies that show that masks (surgical and n95) can help prevent healthy people from getting infected [1][2]. Everyone I've seen claiming the opposite (including supposed experts being interviewed) usually do it without any significant data to back it up (just some high level theorizing). I also rarely see anyone discussing the nuances of efficacy against airborne vs droplet spread viruses. Using just a minimum amount of reasoning it would seem very plausible that masks would be effective against droplets but less effective against airborne diseases.

[1] https://www.newscientist.com/article/dn3692-face-masks-are-b... [2] https://annals.org/aim/fullarticle/744899/facemasks-hand-hyg...

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Public health authorities like CDC don't recommend their use among people who are not infected:

CDC does not recommend that people who are well wear [a] facemask to protect themselves from respiratory viruses, including 2019-nCoV. - https://www.cdc.gov/coronavirus/2019-ncov/about/prevention-t...

Now, I'm not one to blindly trust a government agency, but most of the evidence seems inconclusive at this point, and one thing can't be ignored: in mainland China, use of masks in public spaces is near 100%, yet the virus is spreading rapidly. Outside mainland China, far fewer people are wearing masks, yet the virus is not spreading much at all.

Not quite sure I get the reasoning in that link.

Sure, it's not likely to decrease your direct infection risk.

But it does decrease the risk of you infecting others.

At any given time you can't really know if you're infected or not if the virus is widespread.

Also the mask would presumably be more effective than coughing into your elbow or a tissue, which they do recommend.

So why not wear them? Why recommend them for healthcare workers but not the general public?

I'm wondering if the unstated reasoning is that widespread mask usage freaks people out and increases the chance of large scale panic.

> At any given time you can't really know if you're infected or not if the virus is widespread.

Unless you're in China, the virus is not widespread. I imagine they would change their recommendation if it was.

> So why not wear them? Why recommend them for healthcare workers but not the general public?

The chance that a healthcare worker who is treating a suspected CoV case is in close contact with an infected patient is close to 100%. On the other hand, the chance that a member of the general public outside of mainland China comes into close contact with someone who is infected, whether they're in the rest of Asia or not, is within a few orders of magnitude of 0.00001%.

Yes, totally agree.

I wonder what the rational tipping point would be for mask vs no mask.

1-Since travel is still occuring out of mainland China, your faith in the virus being limited to the nation of China seems misplaced.

2-Your estimates of the probability are unlikely shift properly as the landscape of infection changes rapidly, and is not apparent to the naked eye.

Humans intuitively do not tend to comprehend exponential/quadratic growth. This video outlines it. The main point is to look how late, in this scenario you'd be saying "no problem" and how quickly it goes from fine, to effed. Note: this is not an endorsement on the other items in this channel, I just think this particular explanation is demonstrative.

https://www.youtube.com/watch?v=iIwyMif5EOg&feature=youtu.be...

> 1-Since travel is still occuring out of mainland China, your faith in the virus being limited to the nation of China seems misplaced.

I never said it was limited to the nation of China, I said it wasn't widespread outside of China and a cruise ship, which remains true despite significant travel still occurring.

Humans are also terrible at intuitively assessing risk, and the current panic is a great example of this.

> Humans are also terrible at intuitively assessing risk

Doesn't that also apply to you? Have you looked into when and where testing is performed? In the US, if you don't have a china travel history, they won't test you.

This has an incubation period that is still indeterminate, and in the US and other large countries, they are barely testing. So you literally don't have a way to be sure of what you're claiming--there's just no data, but somehow you are very confident in what you claim?

Have you read up on the Spanish Flu? Was that just a "panic"? So far, by every measure, this looks to be worse--more transmissible, harder to detect, with a higher mortality rate. The Spanish Flu killed between 1 and 5% of the world's population.

> Doesn't that also apply to you?

Yes indeed, and to you also. But in the same way that one can learn to better appreciate exponential growth, one can learn to better appreciate risk, and try to apply that knowledge rationally rather than basing decisions on fear.

> Have you looked into when and where testing is performed? In the US, if you don't have a china travel history, they won't test you.

Yes. The most reliable testing procedures are quite invasive and carry at least some exposure risk for the healthcare worker carrying them out, especially if done outside a hospital setting. They also aren't guaranteed to detect the virus in the early stages, or in minor infections. This is one reason why China has moved to include clinical diagnoses as confirmed cases, and it's also why they didn't just test every person on the Yokohama cruise ship straight away.

> This has an incubation period that is still indeterminate

Not really. There are some pretty good bounds on it, especially with the significant number of cases in Wuhan available as data.

I am confident in what I claim (given that what I claim is quite limited). I'm not making predictions here, I'm talking about the current state of things. Beyond that, let's see what happens...

> I'm wondering if the unstated reasoning is that widespread mask usage freaks people out and increases the chance of large scale panic.

Different cultures and situations handle this very differently. I'm hearing reports in London that people are being attacked for wearing a mask in public.

Meanwhile, if you want to scare everyone around you in Hong Kong, go out without a mask and then cough.

> Public health authorities like CDC don't recommend their use among people who are not infected

See: https://www.cdc.gov/coronavirus/2019-ncov/hcp/index.html

Your link & the CDC don't say what you think they say.

CDC's recommendations are that members of the uninfected public should not wear N95 masks.

This should NOT be understood as: CDC says N95 masks are ineffective at preventing airborne infections of Covid-19.

It IS the CDC saying: N95 masks are non-trivial to use correctly, require decontamination protocols or single-use replacement to avoid infection and contamination from used masks themselves (potentially full of virus particles), and protect against a threat many people are unlikely to be exposed to (close proximity infected persons) -- a mix of criteria that make them inefficient to recommend for general public use.

As you see in the link above, CDC absolutely recommends N95+ respirators for EMS and healthcare workers, when working in close proximity to infected persons.

But healthcare workers have a substantially higher airborne exposure risk, as well as professional support and training for properly using N95 masks.

They do say what I think they say, but yeah, I should have clarified that I meant the public, not healthcare workers. (I addressed this more clearly in another comment on the same submission.)

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