There are many illnesses for which humanity never reached natural herd immunity. Smallpox was consistently deadly for millennia, for example. Malaria's still going strong. HIV is kept in check by treatments, not immunity.
The COVID delta strain has an R of at least 5. Using naive models, this would mean that we'd need at least 80% immunity. But even if we achieved 100% vaccination, it's not clear that current vaccines (or natural infection) can provide 80% immunity over the longer term.
So realistically, I suspect that COVID will simply become one of the risks of life. I fully expect that I will catch it multiple times in the decades to come. But I get an annual flu shot, and I'm willing to get an annual COVID booster if necessary.
And there's no guarantee that this will all blow over soon. The worst case historical coronavirus appears to have jumped to humans around 20,000 years ago, and it looks like it exerted heavy selective pressure over many generations. See https://www.nytimes.com/2021/06/24/science/ancient-coronavir....
"Herd Immunity" as not the correct term to use because yes, it is with us for the foreseeable future.
Some weaker form of "herd immunity" where most people have had exposure and it ceases to become a large scale social threat would have been more correct, but I'm at loss for an exact term.
- Not all vaccines need be quite so targeted.
- Naturally acquired immunity can also be evaded.
If that probability is still lower than without the intervention, it has been eroded, not evaded.
In the case of the vaccine in particular, some level of breakthrough infection is expected, so one case of such is unsurprising
At this point I don't understand why this isn't obvious.
You make a targeted vaccine, in this case it will be evaded. We see it right now. That will continue. Natural immunity will cast a wider net and be proven much more effective.