I think some people will just ever develop immunity. When I was a kid, My best friend caught the chicken pox 3 times before we were teenagers. (This was way before the vaccine.). The doctors told her she would probably never gain immunity from it. She had an aunt who was the same way.
Gena
DS, age 11 and always amazing
“Autistics are the ultimate square pegs, and the problem with pounding a square peg into a round hole is not that the hammering is hard work. It's that you're destroying the peg." - Paul Collins, Not Even Wrong