We still don't know how effective the vaccine is longer term.
Antibodies are important, but so is T cell sensitisation and that is more prominent with the second dose.So waning antibodies may not actually mean you have waning immunity.
The antibodies may decrease, but the T cells may stick around.
There is concerning data regarding immunity coming from Israel, as they ended up vaccinating quite early and they're having quite a few breakthrough cases. We will have to keep an eye on what happens, the data could be an outlier due to other confounding factors, or it could mean that we do need a booster.
But just because we may need another booster doesn't mean we will necessarily need one every year. Hep B, for example, requires three vaccines. And some people just don't respond like other so they require additional ones until they mount a proper response.
Vaccines responses aren't an all or nothing, black and white thing. But requiring a booster is better than getting covid every 180 days (how long natural immunity is thought to wane).
I hope that makes sense, I haven't had coffee yet this morning.
