Selection Pressure and Lethality
Aug. 19th, 2021 06:40 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
writerkitI keep seeing people wave around "viruses evolve to be less lethal over time, therefore it is just a matter of waiting COVID out and no, it's not going to turn into killing off a third of Europe like the Black Death did." Like this is a truism.
It's not. It's true there's no selection pressure for lethality, but if the period of asymptomatic infectiousness is long enough, there's no real selection pressure against it either. And there's definite selection pressure for "vaccine-evasive," which may or may not correlate with lethality. I can even point to a recent example of something that's remained highly contagious and quite lethal: HIV. Which may be less of an overwhelming threat in the US these days, but on a global scale this is a pandemic that's been raging for a few decades and it's never become less lethal. It's become treatable-- both in the sense that having it is no longer a death sentence if you live in a country where you can get a cocktail of expensive drugs and that we now have straightforward post-exposure prophylaxis protocols--but the virus itself has never evolved to be less lethal; absent the drug cocktail it will kill you just as much now as it did back in the eighties.
I get that this is terrifying to think about, but we have no guarantee it's not going to evolve into something with a lethality more like original SARS! As long as it stays contagious enough before you show symptoms, there's no selection pressure against it doing that.
Now, since that was very doom and gloom, I will offer you a ray of science-based hope in the form of this Nature article about how people who survived original SARS produce many more antibodies in response to a COVID vaccine and also produce antibodies to several other zoonotic viruses. They then took this and created a nanoparticle that produces stronger immune response in monkeys than even mRNA vaccines (and that same "other antibodies to diseases they've never been exposed to" effect). This is just a proof-of-concept study with a small sample size, but it's one of the more hopeful avenues of science I've seen.
It's not. It's true there's no selection pressure for lethality, but if the period of asymptomatic infectiousness is long enough, there's no real selection pressure against it either. And there's definite selection pressure for "vaccine-evasive," which may or may not correlate with lethality. I can even point to a recent example of something that's remained highly contagious and quite lethal: HIV. Which may be less of an overwhelming threat in the US these days, but on a global scale this is a pandemic that's been raging for a few decades and it's never become less lethal. It's become treatable-- both in the sense that having it is no longer a death sentence if you live in a country where you can get a cocktail of expensive drugs and that we now have straightforward post-exposure prophylaxis protocols--but the virus itself has never evolved to be less lethal; absent the drug cocktail it will kill you just as much now as it did back in the eighties.
I get that this is terrifying to think about, but we have no guarantee it's not going to evolve into something with a lethality more like original SARS! As long as it stays contagious enough before you show symptoms, there's no selection pressure against it doing that.
Now, since that was very doom and gloom, I will offer you a ray of science-based hope in the form of this Nature article about how people who survived original SARS produce many more antibodies in response to a COVID vaccine and also produce antibodies to several other zoonotic viruses. They then took this and created a nanoparticle that produces stronger immune response in monkeys than even mRNA vaccines (and that same "other antibodies to diseases they've never been exposed to" effect). This is just a proof-of-concept study with a small sample size, but it's one of the more hopeful avenues of science I've seen.
no subject
Date: 2021-08-20 12:12 pm (UTC)no subject
Date: 2021-08-20 12:16 pm (UTC)My understanding from when I took biology 20+ years ago is that there *is* selective pressure against lethality, but that doesn't mean that new emergent viruses become benign in a few decades, it means that viruses that have been around for hundreds or thousance of years tend not to be things like commmon cold viruses, which are not too harmful. If someone wants to "wait out" a few hundred years and a whole lot of deaths... um? I guess that's one way of looking at it? O_O