Stef
Hey Susan! You may be interested to check out Dr. Falconer's blog posts and podcast episodes on titers - I think one is called, "Titers, Are You Using Them Wisely?" There are a few. Anyways, he says that once you have a positive titer for something, you likely don't need to titer again as that proves an antibody response and therefore immunity. He says they're like a pregnancy test - it's a yes or no and the level of the titer doesn't matter and will fluctuate (and usually diminish) over time. He says a diminishing titer number doesn't mean they are losing immunity, but rather that there's no need for the body to keep an active response to a threat that isn't present, but it can boost one right up again if exposed to the thing.