A couple notes:
1. The vaccine is not substantially different from natural immunity. The two main distinctions: a) natural immunity is broader and more resilient due to having multiple targets for antibodies as opposed to just the spike protein, and b) the PCR test is sufficiently sensitive to detect people who never got a substantial infection nor were contagious. These people may not develop broad immunity but also were never contagious so I don’t think anyone cares. I’ve never seen support for the hypothesis that some non-immunodeficient person can be symptomatic and contagious and not develop immunity.
2. The immunity is likely to escape the vaccine first due to all vaccines coding for only one protein. The primary (perhaps optimistic) hypothesis on that front was that evading the recognition of the spike protein would force the disease to be less infectious. I’ve not seen any good evidence for this, nor do I necessarily believe we have the capacity to support such a hypothesis.
3. Immunity doesn’t mean no reinfection, it means shortened period during reinfection, usually more mild symptoms, and less transmissibility (which correlates strongly with severity).
4. The current curve reduction is almost certainly a result of high immunity eg high immunity within the populations frequently interacting.
5. Antibodies are not synonymous with immunity. People have immunity from T-cell memory even after mild infection.
6. It’s unclear to me why immunity “stops,” my suspicion is that the largest force in that equation is evolution of the underlying virus to evade immunity, not some ticking time bomb typically characterized by the mainstream community. I’m not sure why this abstract belief of ticking time bomb immunity has become so prevalent.