COVID spreads most in the few days before and after the appearance of symptoms. Organ failure, lethality, are largely due to the immune response to the virus.

The virus has little evolutionary pressure to be less lethal. COVID has already spread before the symptoms appear.

> Evolutionary pressure selects for less deadly viruses over time.

I'm hearing that for the first time, do you have a source?

> longitudinal risk

With longitudinal I meant the risk of what we have labelled 'long Covid' but really seems to be a conglomerate of different, sometimes chronic diseases in different people, that we still don't really know how to treat effectively (not very frequent in absolute terms, but orders of magnitude more frequent than any serious side effects we have observed due to the vaccines).

So if I understand you correctly, what you are fearing is that there is some unknown risk about the mRNA vaccine, that will only reveal itself over time, but that we have no idea about the mechanism of action nor any actual cases. Is that right?

>> Evolutionary pressure selects for less deadly viruses over time.

> I'm hearing that for the first time, do you have a source?

A virus that kills its host before it has a chance to infect others cannot reproduce.

I cannot remember which virus it was (might have been ebola) but it wiped whole communities so fast it died off because there were no new hosts to infect.

Not sure if that's what parent meant - these are extreme cases. In general (e.g. in the case of SARS-Cov2) evolutionary pressure will increase transmissibility but is indifferent to lethality (again up to the extreme point where lethality precludes transmission).

Won't any amount of lethality preclude some transmission?

In general no, as was remarked in a sibling comment in this thread: SARS-Cov-2 on average spreads within the first 1-4 days after infection (viral titers peak on day 2 I believe), so the virus is indifferent to what happens after.

I also want to remark that there is the opposite effect that transmissibility correlates strongly with viral load (amount of viral particles) and viral load correlates weakly with lethality.