[TomMarius]

It's true though, the mask does not protect you from coronavirus, only a FFP3 respirator will. It prevents you from touching your face and coughing/breathing at others, which is the most common medium. They obviously shouldn't have discouraged the public from wearing masks, but it was not a lie - preventing spread of disease and contraction of disease are very different things. I wouldn't want my doctor to only wear a mask.

[seesawtron]

I think in times of crisis (and in general to some extent), it is difficult and non-advantageous to aim SOLELY to be technically correct because not everyone is willing to pay attention to details. I agree that everything you have mentioned is technically correct but people need and look for simple guidelines and thumb rules from expert.

There has been a huge debate about the goal of statistical tests. Is their purpose to (i) find the truth (the effect you noticed in your experiment and the hypothesis you propose to explain it being true or not), or (ii) help an experimenter in making a decision what future experiments should they do to get closer to the truth.

I see this same debate re-occurring pandemic times. And I would argue that we must aim for the latter because in the end people want to know: Should I wear a mask or not? The former truth can be sought out in non-pandemic times with well-defined studies that are not under time pressure to churn out a publication.

WHO expertise failed to cut through this superficial chaos of "scientific expertise" to help people make that decision early on.

[chrchang523]

Note that, due to "researcher degrees of freedom", statistical tests are a lot more effective at stopping you from fooling yourself than they are at stopping you from fooling others. Preregistration helps with the latter problem, but there's ultimately no substitute for actually replicating the results.

[pinky1417]

Two nitpicks: an FFP2 should also work pretty well with its 94% filtration capacity. Second, I assume you're in Europe, because USA-spec N95 or N100 masks would also work. Doesn't affect the point you're making.

Reason and recent scientific evidence, however, does affect your point that nothing but the highest-rated respirators prevent contraction. The FFP2/FFP3/N95/N100s of the world prevent contraction much more effectively than lower-rated masks or respirators, but it's wrong to say that other masks don't protect against this coronavirus.

Common sense suggest that homemade masks prevent the contraction of COVID, just to a substantially lower extent than the higher-end respirators. Even before the scientific studies came out showing that homemade masks could reduce contraction, it wouldn't be dumb to wear a mask for purely selfish reasons. A bandana blocks some particles. A Chinese spec KN95 is likely better. Even if the bandana only blocks 25% of particles that could cause COVID, I'd definitely wear it if it was all I had and I had to go to the grocery store.

But you don't need to take my word/logic for it. Here are a few pre-prints I found on the great medRxiv. https://www.medrxiv.org/content/10.1101/2020.04.14.20065375v... https://www.medrxiv.org/content/10.1101/2020.05.06.20093021v... https://www.medrxiv.org/content/10.1101/2020.05.07.20093864v...

[TomMarius]

I agree with everything you said except about the protection thing. I would except things that are supposed to protect me from a thing to be capable of it - a bandana, a mask, or a lower-rated respirator protect me from most droplets containing the virus, but have no capability of protecting me from the virus itself. However this is, as another commenter said, probably too much technical correctness.

[P-ala-din]

just to make sure that I'm understanding:

- If using X reduces the probability of contracting P. then X protects you from X. right?

- If a mask prevents you from touching your face and that reduces the probability of contracting the disease. Then masks do indeed protect you.

> I wouldn't want my doctor to only wear a mask.

I feel that this is a strawman.

- - -

but even if we ignore the face-touching, I don't understand how is it possible for masks to make things worse.

if we were talking about bacteria, then yes the bacteria can fester there.

but if the virus is carried by droplets, and a part of these droplets end up on the mask instead of in your nose. then surely that would reduce the probability of being infected right?

[TomMarius]

I never said masks make things worse (with the exception of the doctor) - I think I said the opposite.

My doctor should wear something that has a filter capable of catching the virus, such as FFP3 respirator. When you breathe in, droplets get through the mask (this gets progressively worse as the mask gets wet) - and if the mask is not a FFP3, you're making a bet that none of the droplets that get through are contaminated, because the mask does not protect you from the virus, it merely protects you from some of the droplets around you; only the correct filter will protect you. The virus is around 50-100 nanometers.

[blotter_paper]

It's probabilistic, like everything, but N-95 masks do protect the wearer from particles that small. The CDC purposefully lied to you so that you wouldn't stockpile masks they (understandably) wanted to use elsewhere.

/https://www.semanticscholar.org/paper/Filtration-Performance...

>Consistent with single-fiber filtration theory, N95 and P100 respirators challenged with silver monodisperse particles showed a decrease in percentage penetration with a decrease in particle diameter down to 4 nm.

[tomp]

If the mask stops some droplets (which it obviously does, as it gets wet over time) and some of those droplets carry the virus, then obviously the mask protects against the virus - not 100%, but some percent (just like condoms!).

[TomMarius]

Nope. It protects you from said droplets, not from the virus, which it is incapable to protect you from, unlike a FFP3.

[amanaplanacanal]

But as far as we know, the bare virus does not travel through the air, it only travels in droplets. Although there is some disagreement on how large those droplets are.

[P-ala-din]

I feel like I have a wrong model of how things work.

I'm thinking that for each virus there is a chance that it will infect a cell. The higher the viral load, the higher the number of chances that you will get infected.

a lower number of droplets -> lower viral load -> less chance to be infected.

[tomp]

What is the physical explanation behind this fact, and how come normal masks protect others if a carrier wears it?

[P-ala-din]

if masks don't make things worse, then they can only help.

(to explain more: there is a mechanism by which they help. so for them to not help (in total) , there must be a way in which they make things worse)

[lambdaba]

It baffles me you're being downvoted for this.