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Comment by roenxi | Hacker News Reader

You say that with great confidence and a lack of sources; and I'm guessing we are equally ignorant on the actual physics of how small droplets move.

The details aren't clear on how the virus is spreading. The virus might have multiple modes of transmission. Closing 2 of them reliably a great deal. There are important things to do with "catching COVID" that aren't binary; starting doses likely matter as well.

I'd rather not talk to you in person if you aren't going to cover your face, tyvm :)

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> starting doses likely matter as well.

That is something that I've been wondering about too. I work in biotech but not as a scientist. These things are tricky to nail down as they seem to be very individual specific. Theoretically, in an exponential growth model, it wouldn't matter if you were inoculated with 20000 or 200000 virons, after the incubation period post-infection, you're going to be generating a huge amount, millions and millions, of virus particles in either case. Certainly, if you keep getting exposed, you're immune system is going to get overwhelmed quickly, but for a single event, I don't think it matters.

Viral dose does indeed matter. https://www.nytimes.com/2020/04/01/opinion/coronavirus-viral...

It’s analogous to containing a new virus outbreak before it becomes an exponentially growing pandemic.

Thanks for taking the time to post the link, but it wasn't convincing as it lacked data and other relevant scientific information that I was looking for. Personally, I do not consider the NYT to a reliable source of information, but I know many do so maybe the link will help someone else.

It could give your immune system an extra day or two to produce antibodies before it get overwhelmed.

> The virus might have multiple modes of transmission. Closing 2 of them reliably a great deal.

Sounds reasonable, but how is a face shield a reliable way to close a mode of transmission if people aren’t spitting liquid in your face?

It increases the effective time large droplets need to spend in the air to get to me, and decreases the airflow around me. It's about the same reason plexiglass screens help, and keeping a 6-foot distance helps.

Plus, it stops me from touching my face.

No, it doesn't stop everything, but it's a buck.

> Plus, it stops me from touching my face.

You would be touching your face if you had correctly fitting PPE, because it's uncomfortable. https://twitter.com/gabbyjackson95x/status/12479391789623255...

It’s okay to admit you’re wrong. It’s okay to not understand everything. It’s okay to defer to experts.

So many people on HN and in tech have the same attitude that if they just spend 5 minutes thinking about something then they can intuit an answer and that they must be right. This is a dangerous way of thinking. If anyone took what you’ve been saying as correct they’d be endangering themselves and depriving medical professionals of tools they need.

But I'm getting my opinions from the experts? See [0]. They recommend covering your face. I agree with them that cloth is more effective than a plastic shield but I'd expect a plastic shield to still be better than nothing. You've got to try and stop droplets from leaving your mouth and reaching other people.

A face shield would be better than failing to create a makeshift covering from a shirt for most people and it'd be resistant to decomposing so it could be stored long term in a home. It'd be a reasonable thing to stockpile.

[0] https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-si...

I don’t think it’s reasonable to stockpile given the huge demand for them by medical professionals.

I also can’t imagine a situation where you can order and wait for a shield but don’t have the time or resources to get a surgical mask or cloth.

And obviously the shield alone isn’t going to protect you from particles. And it might not help slow the spread if you’re infected yourself.

But again I’m speculating. If the health professionals say they need them and the public doesn’t, I’ll defer to them. I’m not an expert in their field and I don’t want to pretend to be or cause anyone to think I am.

This is just common sense. Aerosolized particles are not impeded by a shield. A shield is intended to obstruct ballistic projectiles. If those projectiles are aerosolized and are in the air that you breathe, then the shield will offer no protection at all. Even an N95 mask still can let in up to 5% of these particles. What efficacy is a piece of plastic in front of your face going to do against that?

> If those projectiles are aerosolized and are in the air that you breathe

It seems like you're imagining that the mucus and saliva particles would behave like a gas, but it's a suspension of liquid particles in the air, which behaves slightly differently. Think of breathing onto glass -- a lot of the aerosol I expel adheres to the glass. Some smaller droplets may move around it, but it's still preferable to receive a smaller dose of the virus.

>but it's still preferable to receive a smaller dose of the virus.

Could you explain why you believe that? I haven't found anything definitive on this topic.

[I'm no microbiology expert, so obviously take this with a grain of salt :-).]

I'm not sure whether the initial dose affects the severity of the disease, but it seems clear that it at least affects the probability of infection. The individual action hypothesis [1] posits that each individual pathogen has an independent chance of infecting a host, i.e.

    P(no infection | n pathogens) = P(no infection | single pathogen)^n

So if one is exposed to a single unit of the virus, infection is theoretically possible but unlikely. At higher doses infection becomes overwhelmingly likely.

I don't know how accurate the IAH model is, but there seems to be a good amount of evidence that infection rates are at least positively correlated with dose, e.g. [2].

[1] https://royalsocietypublishing.org/doi/full/10.1098/rspb.200...

[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2869824/pdf/120...

Well there's two things. There is the 'minimum viable dose' which you can estimate for various diseases, that will most likely result in an infection. And then there is the dose size (above that minimum).

With an exponential curve, whether you start off with 10,000 or 100,000, given that it takes about 2 weeks for our adaptive immunity to kick in, the virus is going to be in the hundreds of millions in either case.

[I work in vaccines, but not as a scientist, so I'm just trying to absorb as much as possible here..]

Yeah that's fair -- there might be some high-exposure situations (like being coughed on) where infection is very likely with or without a face shield.

I suspect that a lot of airbone infections are from inhaling small doses here and there though, considering how long mucus droplets can stay suspended [1] --

> Particles of diameters 1-3 μm remained suspended almost indefinitely, 10 μm took 17 min, 20 μm took 4 min, and 100 μm took 10 s to fall to the floor.

[1] https://www.mintie.com/assets/img/education/Aerosol%20transm...

There is a good New Yorker article on the matter this week:

https://www.newyorker.com/magazine/2020/04/06/how-does-the-c...

I'm really not a medical expert at all. But, just thinking about it one could at least speculate or argue: A smaller payload means the virus takes a longer time to "become very active" in the body and delaying this "ramp up" period may give your body's immune response a longer lead time from when it first "sees" the virus to when it becomes dangerous to you.

Well with an exponential curve, even if the amount of the initial dose changes 10 fold, from 20,000 to 200,000 virons you will get to hundreds of millions in pretty much the same time. I believe adaptive immunity takes about a week or two to kick in, and in that time the virus is going to keep multiplying like crazy, regardless of the dose.

Also, suppose you were living with a partner and both of you got infected. Both of you will continually shed and "re-infect" the other, so would we expect that the infection will necessarily be severe?

Stop spreading FUD.

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