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Originally Posted by blankall
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PCR cycle counts aren't really a great proxy for viral load or replication levels. They pick up dead and neutralized virions, which is why you can test positive for months after recovery. Only culture tests which determine the level of live virus are useful for determining this, and they have repeatedly shown that immunologically naive people have significantly higher viral levels.
And of course, even if peak viral load was similar, the duration of infection (and replication) is shorter with prior immunity, so the total number of replications is lower.
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Exactly...it has to overcome existing immunity, which is what we don't want, and only likely to occur in someone who already has immunity. Once again, without immunity, there's no selective pressure to overcome immunity.
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It has to overcome it, but it doesn't make it more likely. Mutations are random, so the threshold for a new variant to spread is higher with immunity. So yes, there is evolutionary pressure to evade immunity, but because immune evasion generally requires a fairly significant number of mutations, the bar is higher.
And ultimately, partially overcoming immunity isn't necessarily a big deal, as long as there isn't a corresponding increase in severity. That's what we see with other coronaviruses.
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Very wrong. People with severe infections go to the hospital and are isolated. People with very mild or no symptoms walk around, go to work, get on transit etc....
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It normally takes a week or so of someone being infectious before they end up with a severe infection, and for much of that period there is little distinction between mild and severe COVID. That and pre-symptomatic spread are things that make COVID so infectious.
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Being less severe would increase the chance of a mutation, as it increases the chance of spread. These viruses have been around for centuries, so your argument about having less mutations due to less transmissions is non-sensical.
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You're misunderstanding what I said. You asked why other coronaviruses haven't randomly become deadly, and why COVID would be more likely to do that than the other circulating coronaviruses. I said, that's because they're far less severe. To become deadly like COVID is, they'd have to become vastly more severe as a result of a mutation, which is basically impossible for any coronavirus, barring a recombination with a more severe variant (which is exceedingly unlikely in humans).
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No. People are still catching them. They still have large viral loads. The viruses have been around for centuries, as you state, that's a lot of transmissions over that time.
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But the rate of mutation is lower for the reasons I outlined (immunity reducing the genetic diversity and allowing the body to neutralize the virus faster).
They also may be inherently more stable too, but it's hard to know that so early into SARS-CoV-2's existence. Though it is speculated that the Russian Flu in 1889-1890 was actually the introduction of the OC43 coronavirus into the human population. But once it circulated enough, there were no longer immunologically naive people (other than infants) so the burden dropped significantly over the years.
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Immunity encourages the bad mutations, which relate to immunity evasion. And, once again, there's no evidence to show that vaccinated people have decreased viral load. That's simply not the way vaccines work. Another paper on the subject:
https://www.thelancet.com/journals/l...ted%20contacts.
Vaccination does not decrease replications, it just helps your body clean them up quicker and with less dangerous elements of the immune system. For example, someone without immunity would rely more on fevers, inflammation, mucus, inflammatory systems, cytokines, etc...which can be quite damaging, and, in fact with Covid are likely the cause of most deaths. People with immunity will rely more on B-Cells, anti-bodies, T-Cells, etc...which can be less damaging (obviously there are exceptions, see HIV).
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Think about the bolded for a second. So vaccinated/previously infected people are infected for a shorter period of time, yet that doesn't lead to fewer replications? How does that make any sense?
Again, the proof is really in what we're seeing. If immunity encourages dangerous mutations, then why was the rate of new variants of concern per infection vastly higher in the first year of the pandemic compared to now? We should have seen 10-20 changes equivalent to Alpha, Delta, or Beta based on the number of post-Omicron infections. And why haven't we seen significant mutations in the other circulating coronaviruses over the decades?
The answer is, an immunologically naive population is like a blank canvas. The virus will mutate and basically any type of mutation has the chance to become dominant. So if it mutates to become more severe, well there's nothing to really stop that as long as it can spread effectively. But with immunity, if it randomly mutates to become more severe, chances are it will die out almost immediately (and before being detected) as it hits a wall of immunity.