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The effect that viruses mutate to become less deadly over time only counts for a specific subset of viruses. The evolutionary goal for a virus is to have more

The effect that viruses mutate to become less deadly over time only counts for a specific subset of viruses. The evolutionary goal for a virus is to have more copies of itself. Killing a patient 3 days after infecting them is a poor strategy for this, so the only option for these kinds of super deadly viruses is either kill a population outright and die out with the population (dead people don't spread viruses), OR if the virus is lucky it will mutate into a less deadly variant to be able to spread to more people. The specific subset of viruses that will evolve to become less deadly have two properties: 1) They kill quickly 2) They kill most people The problem with Covid is that it doesn't have these properties. It's only deadly for approximately 1% of the population, so it will continue spreading even if it ends up killing the host, because for every 100 people only 1 has stopped spreading. The other problem is that Covid doesn't kill quickly, if I recall correctly, most people die after week 2-3. Covid will spread even before the host is symptomatic, so again there is no evolutionary advantage to mutate away this trait.

rossdavidh 5y ago
1) if people with mild or no symptoms keep moving among the population, but people with severe symptoms stay at home, then there would be a strong evolutionary pressure to cause milder symptoms 2) "dead people don't spread viruses"...UNLESS it's a zombie virus
- merrywhether 5y ago
  Your 1) only matters if transmission is related to symptoms. If the virus is transmissible for a while before the symptoms like Covid, symptom severity matters less (pre-symptom R-value gains outweigh post-symptom R-value losses). Reductively, if you’ve already infected your social circle pre-symptoms, what happens next is much less relevant to the virus’ lifecycle.
  - rossdavidh 5y ago
    Even if symptoms don't impact transmission directly, if you're out circulating in the population (as opposed to self-isolating or in the hospital), you'll be able to infect more people. Unless, of course, self-isolation or quarantine are entirely ineffective, which is not totally out of the question but I think people staying at home probably do spread it at least a bit less than people headed to the grocery store.
- peter422 5y ago
  The mildness or severity of symptoms is determined after the period of maximum contagiousness. What you are talking about sounds nice in theory but it doesn’t really add up based on how this virus works. If anything there is a pretty strong argument the other way… a more contagious version of covid will probably have a higher viral load and this probably lead to higher chance of serious disease be (like delta).

rossdavidh 5y ago

1) if people with mild or no symptoms keep moving among the population, but people with severe symptoms stay at home, then there would be a strong evolutionary pressure to cause milder symptoms 2) "dead people don't spread viruses"...UNLESS it's a zombie virus

merrywhether 5y ago
Your 1) only matters if transmission is related to symptoms. If the virus is transmissible for a while before the symptoms like Covid, symptom severity matters less (pre-symptom R-value gains outweigh post-symptom R-value losses). Reductively, if you’ve already infected your social circle pre-symptoms, what happens next is much less relevant to the virus’ lifecycle.
- rossdavidh 5y ago
  Even if symptoms don't impact transmission directly, if you're out circulating in the population (as opposed to self-isolating or in the hospital), you'll be able to infect more people. Unless, of course, self-isolation or quarantine are entirely ineffective, which is not totally out of the question but I think people staying at home probably do spread it at least a bit less than people headed to the grocery store.
peter422 5y ago
The mildness or severity of symptoms is determined after the period of maximum contagiousness. What you are talking about sounds nice in theory but it doesn’t really add up based on how this virus works. If anything there is a pretty strong argument the other way… a more contagious version of covid will probably have a higher viral load and this probably lead to higher chance of serious disease be (like delta).