Except that it is believed that COVID vaccine protection wanes with time. Hence the booster six months after completing the initial vaccination.
I spoke to my doctor about this and he gave an analogy that I find helpful. Vaccines create anti-bodies and memory cells, assuming you have a functioning immune system.
Anti-bodies are like front line soldiers with weapons loaded and in-position. If the bad guys attack (you get exposed to the virus) the front line usually engages immediately and the battle is usually short lived. However, over time the front lines are sent home so the borders are left open. Meanwhile, the base kept records of how to fight the bad guys in case they have to do it again. So, say 6-9 months after vaccinatioin (as is the case with covid vaccines) the front lines are open and if an attack occurs the home office (base) needs to figure out what they did last time and call in the reserves and train new recruits. This can take some time, so depending on your immune system you may or may not get sick. However, once the forces are built back up you usually (again depending on your immune system therefore how quickly anti-bodies were reconstructed) win the battle, and thus have anti-bodies on the ready again.
So, I got the booster mainly because I wanted anti-bodies ready to go. The question is: Are you sure you're healthy? That answer can only be determined with a thorough physical examination that includes much testing.