The flip side is that delta is very likely optimally transmissible/virulent. Once immunity is built up to delta, then it'll be forced to evolve to achieve immu

The flip side is that delta is very likely optimally transmissible/virulent. Once immunity is built up to delta, then it'll be forced to evolve to achieve immune escape and that'll make it mutate much more than it has and pick immune escape mutations that will make it "worse" in the immune naive population. Immune escape will come at a cost. And the scientific evidence of "waning immunity" in the headlines these days is likely wrong and a gigantic lesson in confounding factors. The HCoV-229E common cold coronavirus evolves to escape immunity, and this one probably will as well: https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1009453 https://journals.plos.org/plospathogens/article?id=10.1371/j... So our immune systems will evolve and take the edge off of all future coronavirus infections, but the virus will also have to evolve and be forced to make tradeoffs and will become less virulent in the process. So if you caught one of the common cold coronaviruses right now and had zero inherited immunity to it, then it would probably still be somewhat mild since it would have been evolving for hundreds of years to be more stealthy than virulent. If you caught the original pandemic version though it would probably suck about as hard as SARS-CoV-2 right now.