Immunity to Covid 19 involves more than just antibodies. Antibodies are more easily measured than other aspects of immunity. There are no commercially available blood tests that will let you know if you have immunity to Covid 19. That’s one of the reasons that measuring antibodies is not recommended. You can’t make good decisions with bad information. In particular, one should not latch on to the news summaries of scientific publications. Studies that show that one vaccine produces higher levels of antibodies after administration require thorough vetting done by experts. Antibody levels drop after administration of any vaccine, but that doesn’t mean that immunity goes away. Since Covid 19 is a novel virus, we don’t have all the answers as far as how long the effect of vaccines last. Many people don’t think we all need boosters and that third vaccines should be reserved for those with compromised immunity who likely haven’t responded to the first two doses. Here is an interesting article which gives a pretty good explanation of the complexities of cellular and humoral immunity form this mornings TPR.