Weird, I've yet to get chicken pox/shingles, mumps, polio etc despite being vaccinated against them as a child. And I still catch the flu regularly despite having already had it.
We obviously do not know yet whether we can get permanently robust immune response to SARS-CoV-2, either from vaccines or from natural infection; the virus is only two years old. We know that we can get permanently robust immune response to the viruses you mentioned in your post. But this cannot be easily generalized to any new virus that comes along.
That’s why the new push is for ‘booster shots’.
The original strain upon which the current vaccines are based has basically died out and Delta carries a lot more viral load (400x or so?), which changes the game a bit.
In comparison, smallpox virus was pretty much the same across centuries, so it was comparably easy to target and eradicate. No animal hosts helped, too.
Pfizer themselves have performed studies that show immunity declining. I do know that they tell from the levels of antibodies seen in blood but I don’t know if the effect of variants has been measured (if it can be measured at all without unethical experiments).