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Originally Posted by calgarygeologist
Speaking of variants, what happened to the rapidly emerging new variants that we saw last year? There has been no talk about variants anymore and previously seemed like the next new variants that was going to wipe us out was popping up every 6 or 8 weeks.
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Widespread immunity tends to depress the rate of new variants of concern. Substitutions/mutations happen all the time, so with little to no existing immunity, a virus just needs to mutate to become more severe without impacting its ability to spread and then you have a very real risk of a more severe variant taking over.
But once the population has immunity, then the viable pathways of mutations are much more limited. So at a given substitution rate (which is relatively constant in a virus) you'll see a slower rate of new variants with higher levels of immunity (at least variants that spread widely). Basically, mutated versions of the virus are now far more likely to hit dead ends than before and only the ones that can evade prior immunity have any real chance of success.
And that's exactly what has happened. We saw Alpha, Beta, Delta, and Gamma emerge (with significant variations in severity and transmissibility) in the first 100 million or so infections. But post-vaccine/Omicron, we've seen billions and billions of infections with little change in severity.