I don't have any experience sorry but I've recently had my immunity to rubella checked (as I'm pregnant) and I am immune.. However, when I had it checked in 2009 during my pregnancy with DS I had borderline immunity. What the? I don't know how I could've suddenly gained immunity when the last time I would've been vaccinated was when I was 12? 13?
Anyway, just thought that was interesting! Probably a useless tidbit for you though!