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Comment by Bnshsysjab | Hacker News Reader

As someone who hasn’t followed, and I understand I’m asking a random internet user this and not a scientist, but what is the definition of ‘prolonged exposure?’ Are people who contract the disease less likely to die that someone who is in close contact for a prolonged period of time? How long is that period? 15 minutes? Two hours?

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Not a scientist, I can only attempt to retell what virologist Prof. Christian Drosten from Charité Berlin told in in his podcast[1]:

It's not really clear at the moment but it could be due amount of dose (more virus particles, faster replication) and where the virus makes contact with the body (if you are unlucky you are breathing a high dose directly into your lungs i.e. coughing patients in a hospital) - your immune system does not know the virus and it takes a while until it's able to fight it off and if the virus is directly in the lungs or you've got a high dose it has less time to do so. If you have it only in the throat it takes a lot of time, like multiple days until it goes into the lungs (if at all, this is also not clear when and when not this happens) and he suspected that in this time period you already have a better immune response.

Besides that (not from the podcast) I've read that the virus can induce inflammation that can can cause blood clots and other nasty things - so you may die from stroke or heart problems and not pneunomia.

There was also a paper that hypothesized that the virus can either replicate in the throat and go the lungs but it's probably also possible for the virus to use the nervous system to reach the brain via the olfactory bulb.

China did isolate ill patients from their families and it was hypothesized that sharing a bed/room with a sick person is a bad idea because the virus is in high doses in the air. So you can read that you should keep fresh air flowing in and possible avoid too much direct contact.

1: https://www.ndr.de/nachrichten/info/podcast4684.html (only in german)

To wit; if my wife gets sick and I care for her, does that mean I am experiencing "prolonged exposure"?

Yes.

Being around a positive person continually for several days at home would mean a lot more exposure than many people would get when encountering others in public.

Maybe? No one knows for sure. We can't directly measure the dose of virions each person receives. There is a huge variations in contagiousness between patients based on factors that are still unclear. Proper use of PPE by caregivers can also have a huge impact.

Yes. Separate as much as possible, don't share a bathroom at all.

I my experience most houses and apartments in Japan, and SF only have 1 bathroom.

It’s dose. So you get a higher dose the longer you are exposed. A smaller dose infected less cells are initially infected and maybe you get less sick. Higher dose may mean you get more sick.

Does it not logically follow that if the dose can be precisely controlled, it could help your body start developing antibodies sooner?

That's the idea behind "variolation", which was used before there were vaccines. It's risky, since you might get infected anyway, or perhaps the dose isn't enough to work.

Making strong guarantees that people will become immune and won't be infected is part of what makes coming up with a vaccine hard. It's apparently pretty easy and quick to come up with vaccine candidates.

With variolation it was not lower dose, but different (mild) strain (cowpox), which offers cross-immunity to smallpox.

It was a controlled infection with Smallpox, by scraping the skin with pus or scab powder from an infected person. Cowpox is what makes the smallpox vaccine.

You are right.

If we have a vaccine candidate that is safe, is there any reason not to give it in mass before knowing if it works? The only thing I can come up with is it takes longer to prove safety than effectiveness, but I don't much about this.

> If we have a vaccine candidate that is safe, is there any reason not to give it in mass before knowing if it works?

Yes. In some cases, the wrong kind of immune response can cause antibody-dependent enhancement (https://en.wikipedia.org/wiki/Antibody-dependent_enhancement), where the immune reaction enhances the severity of the virus.

This is not terribly common, but alas this exact mechanism has been seen in earlier work on SARS.

Also, during the H1N1 scare a vaccine used in Europe caused some people to develop narcolepsy (though perhaps more would have gotten it from the virus itself without a vaccine). It can be hard to determine that something is “safe” quickly.

SARS-CoV-2 is also at a really awkward point in the fatality curve (with the best estimate of the IFR being around 1%) that you really want to do something, but you also can't really accept a significant chance of that something having a significant side effect.

Dosing is a thing. There are high dose and low dose influenza vaccines for example. But even then immunity isn't guaranteed, you need neutralizing antibodies to develop as well. Lots of things have to go right to get a sustained safe and effective response which is why vaccines take so long to develop.

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