From what I can remember from my immunology class, B-cells specific to a particular antibody will detect the antigen in a re-infection, start to massively clone

From what I can remember from my immunology class, B-cells specific to a particular antibody will detect the antigen in a re-infection, start to massively clone themselves and quickly increase the specific antibody titer in the blood in response. It doesn't make sense from an energy point of view for these to get produced in large volumes in the blood forever, so unless you're continually re-infected, the antibody titers will then drop but the memory B-cells remain, ready for a new round. What's crucial is how fast the immune system can ramp up again in a re-infection, perhaps for COVID19 this is almost always fast enough to prevent a deadly re-infection but not fast enough to prevent any form of viral replication and shedding and this is why vaccinated still spread the virus around (and this might keep being the case with the current type of vaccines for corona viruses unless you deal out 10 billion booster doses every quarter). So the question is complex and depends on what your goals are, and all of this has to be dumbed down in a way for consumption by the general public who just want to know "how long is my vaccine good for"... :/ Perhaps the antibody blood titer is not the only data that is relevant, but maybe it's determined that it correlates to one of the outcomes in a good enough way..