I'm another who can't maintain an immunity to rubella - I had MMR boosters after both DS1 and DS2 were born, and I STILL have no flippin' immunity according to blood tests earlier in this pregnancy. I'm opting not to have another MMR booster - I'm not planning another pregnancy (DH going to have a vasectomy soon-ish, I think/hope), so I can't see the point. Just my thoughts on my situation though