I think the Germans (starting with Christian Drosten last year) have been a bit better at spelling out what endemic means: you will get antibodies against covid either from the vaccine, the virus, or in the long term both.

It's all pretty much guesswork at the moment, but this struck me as a reasonable guesstimate
- without vaccination immunization lasts 550 days so you can expect to get covid once every 825 days (~2.5 years) - as you don't catch it as soon as your immunity wanes.
- with high vaccination uptake (inc boosters) the transmissibility is reduced ~75% and disease by ~50% so you can expect to get covid every 3300 days (~9 years).

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