Now you're vaccinated, how will you know when your immunity runs out? Will you keep going for antibody testing until you have none left?

The sole absence of antibodies does not determine immunity against disease once vaccinated or acquired through natural infection. If immunity is present with vaccines then upon exposure to the virus the body uses memory cells to jump start production of antibodies real fast quick enough to provide protect against disease. We don't know how long antibodies last with the vaccine. The other arm of the immune system is also activated and that is cellular immunity for which antibody test do not detect. Immune cells destroy infected cells. 

The vaccine produces both an antibody response and cellular response that provides protection against the virus. 

At present the sole determinant of immune status is not strictly antibody testing. 

Just use your common sense. If you feel bad, then maybe it's run out, right??

No, I'll watch the data. I check the Johns Hopkins site every day. As more people get vaccinated, the transmission rates are going down. When there are no more new cases, it will be perfectly safe not to be vaccinated. The virus has to have human hosts to survive and be passed on. If the virus is still around, and the scientists say that we need a booster, I'll get one. Many people get flu shots every year, you know. 

i think your doctor will let you know

i think your doctor might tell you