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Comment by daxfohl | Hacker News Reader

Is it possible that a very very low exposure can cause your body to ramp up an immunity response? I'm wondering if fatality rate has gone down because most people by now have had some exposure to the virus: not enough to get sick (not even asymptomatic), but enough for the immune system to prep that something is in the environment.

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I'm curious about this too. I'm no epidemiologist, but as I've kept walking around my low-to-mid-density DC neighborhood I've wondered, if an exposure level likely to cause symptomatic illness is on the order of a minute's close contact with a sick person, then maybe it is good to get a second or two of exposure per week?

I feel like this is more of an immunology question, and really it depends on the amount of a viral load you would need to elicit an immune response without systemic signs and symptoms. And then you're basically reinventing the wheel of vaccination.

Yeah, IANAE also, but I half wonder if this is how a new variant of regular flu gets started. Kids immune systems handle it like any kind of flu virus. The older you are, the weirder this thing looks to your immune system, and less likely able to handle it. If you're introduced to it slowly, the more able your immune system is able to figure it out.

So I'm wondering if this thing never goes away, the vaccine never works 100%, but in a year or so it's not much different from any flu in all age groups.

Will that's essentially what happened with the OC43 coronavirus so there's a good chance it will happen again.

Interestingly NYT is running an article about this now: https://www.nytimes.com/2020/09/08/health/covid-masks-immuni... (TLDR: plausible, but nothing conclusive)

Fatality has gone down because we are testing a much higher percentage of infected people. When 20+% of tests are positive you’re testing seriously ill people. When ~4-8% of tests are positive your testing people who may recover before becoming seriously ill.

See: https://en.wikipedia.org/api/rest_v1/page/graph/png/COVID-19... from https://en.wikipedia.org/wiki/COVID-19_pandemic_in_the_Unite...

That doesn't explain western Europe, where for example France has gone from 1000 deaths per day to 10, with the same infection rate in the 2nd wave. If this was due to just testing, that would imply testing was off by 2 orders of magnitude, which would imply half of the population has already contracted the virus, which we know from antibody testing is not the case.

https://www.worldometers.info/coronavirus/country/france/

You see the same thing in New York, where fatalities per day has gone down from 1000 to 7, while cases per day is only down 90% from peak. Crowded cities it may be impossible to avoid exposure completely (which crazily may be a benefit!).

https://www.worldometers.info/coronavirus/usa/new-york/

Rural US is where the fatality rate isn't going down much, which would make sense since there's higher chance of someone having had zero exposure to the virus and then getting a bunch of it at once by coming in contact with a sick person.

NOTE this is not based on any research other than some guesses as to how these numbers could line up. Do not use this as a source for anything!

> which would imply half of the population has already contracted the virus, which we know from antibody testing is not the case.

Antibodies disappear quickly so antibody studies aren't a perfect indicator of spread.

See for example:

> The UK study, meanwhile, suggested that antibodies could disappear completely within three months. The research tested more than 90 coronavirus patients for antibodies over 94 days. The results showed that three weeks after infection, just 60% of patients had developed a "potent" antibody response. In the weeks that followed, a mere 17% of those patients maintained that level of antibodies, The Guardian reported. In the other patients, antibody levels declined 23-fold or became undetectable within three months.

https://www.businessinsider.com/coronavirus-antibodies-last-...

There are many factors:

- more testing, as you said

- the most vulnerable people are already dead, and those who aren't are taking extra precautions

- currently, most new cases are from younger people, less vulnerable

- we are becoming better at treating it

Less viral load because of masks is just one other factor. There may be others, like weather or mutations.

Note that even a single viron can cause disease, as per [1]. Maybe a trickle of tiny doses could help trigger an immune response, but there's always a risk of getting sick before then.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2677602/

If only they made vaccines that way.

Vaccines are usually dead or mostly-dead or otherwise-modified things. It's not just low counts of live viruses.

Your clarification was less correct than what you replied to.

Vaccines are not all attenuated. Often they are killed. See https://en.wikipedia.org/wiki/Inactivated_vaccine for more on that.

It's interesting that the word used for inactivated viruses is "killed" rather than, for instance, "destroyed". Destroyed might not be a better word choice because it may imply that the structure is completely taken apart but point being: (not to throw semantics into the mix just for kicks) does modern science consider viruses to be alive?

> does modern science consider viruses to be alive?

This is a (bad) philisophical question for people who do not understand the concept of "spectrum", not a scientific question.

I don't believe there is such a thing as a bad philosophical question. Perhaps some questions aren't yet worth the time investment to think about. When we engineer self-replicating machinery (or rather, before then) this caveat is worth defining.

I disagree.

Deciding where on the spectrum between non-life and life we declare something to be alive is endlessly debatable and non-actionable. The fact that in time technology will add more points on that spectrum does not change this fact.

The precursor to modern methods was to obtain a little bit of smallpox and inoculate yourself with it. It was vastly less deadly than being exposed in the normal course, though not really safe. It still demonstrated the principle, that a little bit of smallpox was quite a lot safer than being exposed to a lot of it. This is not a good idea generally, it worked on smallpox when there was no other option. Still, dose can absolutely make a difference in how deadly a virus is.

https://en.m.wikipedia.org/wiki/Variolation

The first real vaccine was to inoculate with cowpox instead, which was safe for humans but induced immunity to smallpox as well.

Modern methods are substantially safer, usually by entirely deactivating the virus before using it, but there are still some vaccines that use live virus (the oral polio vaccine is a live attenuated virus).

Perhaps GP is not aware of how vaccines work. You should seriously answer the question.

But yes, that is how vaccines work more or less. Though I believe the virus in the vaccine is either dead or incapacitated in some way.

That is how vaccines can work. I think that saying "more or less" is disingenuous, when there are also toxoid, subunit, or conjugate. None of these broad classifications mention the adjuvants that are present. Look at the mRNA vaccines that are being tested for sars-cov2, such as by Moderna. Vaccines are not always attenuated or inactivated.

Yeah if only but they do not.

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