Since covid 19 is new. No one really knows how much time a booster can give or if it'll be similar to flu when each year there will be a need to a shot relevant for this year variants.

What so far seems reliable enough is that the vaccination itself reduce chance for complications when you do get it.

Not enough time has elapsed to say, but it certainly does appear to put immunity back up to original levels, which were against wild-type, even though delta is worst.

https://www.nejm.org/doi/full/10.1056/NEJMoa2114255

Hep B is a 3 shot vaccine. One of the medical podcasts I listen to is speculating that maybe it was always going to take 3 shots with Covid.

Completely wild speculation, but I think it will be more than 6 months, because covid variance is much less than flu.

There is emerging proof that dissease+vaccine immunity is much better than dissease or vaccine alone, but it might also be the booster effect.

After all, there are other vaccines -- such as hepatitis B where you need a booster after one year (booster 3), before you get your long-lasting antibodies.