I'll take a shot at this. The short answer is Zeno's paradox, known by ancient Greeks. Basically, if every generation (infection, incubation, recovery) of Covid results in the next generation being smaller, eventually Covid dies out. And, most of us never get an infection. You can see this in recent extinction of many species on Earth. They kept reproducing "round and round," but didn't reproduce enough and became extinct.
We don't technically know the answer for Covid yet, but for most other diseases we vaccinate against, those diseases die out. We occasionally get small outbreaks due to foreign reintroductions, but those too die out. It will probably be the same for Covid. Most likely we need to vaccinate kids to get there. Then Covid will die like a hunted dodo bird. Covid vax will be added to the childhood immunization schedule to keep it dead. Maybe there will be an adult booster like MMR. On into the future, very rarely a few people will get Covid infections introduced from overseas or other reservoirs. Like measles and whooping cough, these will mostly occur in anti-vaxxer groups, though there will be some breakthrough cases as well.
It's possible the current vaccines don't work well enough against infection, or protection fades too quickly, or we fail to get enough of the population vaccinated. So far, we're 50% vaxxed, and the experts were saying we need to get above 70%. Since delta, most think the threshold is yet higher. Nobody knows precisely. Mathematically, the higher we get vax rates above the threshold, the faster Covid goes away and the better we resist future outbreaks. I think we'll make it, and it's far too early to say we won't.
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