Your antibody level will determine how likely you are to become infected and also, to a lesser extent, how likely you are to have a severe case. Keep in mind you need a lot more antibodies to prevent infection than you do to prevent severe disease. Unfortunately we now know protection against infection is short lived after vaccination (a couple of months) whence why people are concerned about the numbers. However, protection against severe disease and death are certainly going to last significantly longer and I think this protection is being undersold.
The question is how long the B cells (and don't forget T cells!) will last to protect against severe disease. They certainly will last more than a year, but we don't know if there will be appreciable numbers at 5, 10, 20 years or longer to protect against severe disease. That's why some vaccines require regular boosters (like the Tdap that is given every ten years or after exposure) to replenish the B cell and T cell populations that normally die off. It is too early to say what time periods COVID vaccines will be necessary going forward, and what the vaccination schedule will look like for optimal results. I wouldn't be surprised if we see recommendations that mix different vaccine technologies like adenovirus vector (J&J), mRNA (Pfizer, Moderna), subunit (Novavax) and perhaps other technologies that are currently being explored (DNA vaccines, for example) and hammer down scheduling when the shots should be given. We are a long way away from knowing what the optimal solution is here, and we are years, perhaps decades away from fully understanding it unfortunately.
Affinity maturation doing work.