Quote:
Originally Posted by blankall
Doesn't change the fact that the next strain that needs to spread, will have to be one that mutates to avoid existing immunity, and that is only likely to occur in someone with existing immunity.
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Not necessarily. Immunity against infection wanes in coronaviruses, and other coronaviruses continue to spread year to year without significant mutations that result in immune escape. For instance, OC43 (the most common human coronavirus pre-COVID) has had single genotypes dominate for up to a decade.
And even if it is the case that immune evasion is the only path it can take, based on the evidence from other viruses, the process will most likely slow down (and it probably already has as I've said above). Recently emerged viruses will tend to display a much more rapid mutation rate that more closely matches their rate of substitution, and this is even more true when there's extremely rapid growth in infection numbers. Only when they are subject to more evolutionary pressures will purifying selection tend to quash deleterious mutations. That has been shown in previous flu epidemics as well as with the limited evidence we have from SARS-CoV-2.
So over time, evolutionary pressures will point mutations in a certain direction (i.e. immune evasion), but they will also significantly reduce the viability of most mutations that do occur, slowing down the overall rate of deleterious mutations.