I don’t think immunity is cumulative. If there is immunity gathered in August of last year to Delta, it will be 6 months old about now and thus begin to crash in effectiveness.
Keep an eye on the monthly study updates from the REACT people in London (Imperial Univ or something). Their most recent report said about 5-10% of current cases had documented pre-infections of over 1 month old. Get to 6 or 8 and dying starts.
And this is purely age. Not variant, the next one of which is due about now.
Usually as one tails off the next one is apparent. There is currently no clear variant on the horizon, so I respectfully disagree. Omicron was the natural vaccination that finished off this pandemic, which is how you would generally expect a pandemic to end.
I think we are done.
You seem to be discounting long lasting memory B cells and T cells.