3 ms·

> People getting a cold on a regular basis dont generally lead to super-colds. This is actually a good point applicable to the broader context, that I hadn't r

> People getting a cold on a regular basis dont generally lead to super-colds. This is actually a good point applicable to the broader context, that I hadn't really thought about. Billions of people get cold/influenza infections every year. Why don't we see more mutations of strains that are highly virulent/tending to more severe outcomes?

bawolff 5y ago
To be fair, influenza is a bit of a different beast than colds, it mutates a lot relative to other diseases. We do get bad strains of influenza from time to time. Most famously in 1918, but we had a flu pandemic as recently as 2009.
- kenneth 5y ago
  Influenza can cross species boundaries and that's what tends to make it generally more dangerous than the natural mutations in seasonal flu. The "swine flu" pandemic of 2009 involved bird and pig influenza viruses mixing genetic materials with human influenza.
tsimionescu 5y ago
Because there is no evolutionary pressure on viruses towards more severe outcomes - if anything, the opposite is true. Higher virulence is occasionally seen though, as was the case with the swine flu some years ago.
- Marsymars 5y ago
  > Because there is no evolutionary pressure on viruses towards more severe outcomes - if anything, the opposite is true. I get this, but it doesn't intuitively follow to me that the incidence of severe strains would be as low as they are. The evolutionary pressure against severe strains shouldn't be enough to stop them from emerging in the short term. And yet, for example, all the severe coronavirus strains seem to be zoonotic, rather than mutations of strains already circulating in humans. > Higher virulence is occasionally seen though, as was the case with the swine flu some years ago. I guess higher virulence is also hard to measure. If there's a rhinovirus strain one year that infects twice as many people as normal, who's going to notice that?
  - bawolff 5y ago
    I imagine that with normal virus evolution, many people already have at least partial immunity to the new strain as its a minor change, where if it crosses the species barrier that's a bigger "jump" so probably nobody has partial immunity so its more unchecked. (Just pure speculation. Not my field)
    - XorNot 5y ago
      COVID-19 is unique in the sense that it sits in a neat "uncanny valley" of virulence and lethality where it's able to attack our healthcare infrastructure (aided by modern travel), but is sufficiently non-lethal that it can keep spreading. The notable issue with SARS (which was incredibly lethal) was that the incubation time was too short - one or two days before you weren't going anywhere, way too high visibility.

bawolff 5y ago

To be fair, influenza is a bit of a different beast than colds, it mutates a lot relative to other diseases. We do get bad strains of influenza from time to time. Most famously in 1918, but we had a flu pandemic as recently as 2009.

kenneth 5y ago
Influenza can cross species boundaries and that's what tends to make it generally more dangerous than the natural mutations in seasonal flu. The "swine flu" pandemic of 2009 involved bird and pig influenza viruses mixing genetic materials with human influenza.

tsimionescu 5y ago

Because there is no evolutionary pressure on viruses towards more severe outcomes - if anything, the opposite is true. Higher virulence is occasionally seen though, as was the case with the swine flu some years ago.

Marsymars 5y ago
> Because there is no evolutionary pressure on viruses towards more severe outcomes - if anything, the opposite is true. I get this, but it doesn't intuitively follow to me that the incidence of severe strains would be as low as they are. The evolutionary pressure against severe strains shouldn't be enough to stop them from emerging in the short term. And yet, for example, all the severe coronavirus strains seem to be zoonotic, rather than mutations of strains already circulating in humans. > Higher virulence is occasionally seen though, as was the case with the swine flu some years ago. I guess higher virulence is also hard to measure. If there's a rhinovirus strain one year that infects twice as many people as normal, who's going to notice that?
- bawolff 5y ago
  I imagine that with normal virus evolution, many people already have at least partial immunity to the new strain as its a minor change, where if it crosses the species barrier that's a bigger "jump" so probably nobody has partial immunity so its more unchecked. (Just pure speculation. Not my field)
  - XorNot 5y ago
    COVID-19 is unique in the sense that it sits in a neat "uncanny valley" of virulence and lethality where it's able to attack our healthcare infrastructure (aided by modern travel), but is sufficiently non-lethal that it can keep spreading. The notable issue with SARS (which was incredibly lethal) was that the incubation time was too short - one or two days before you weren't going anywhere, way too high visibility.