I had an MMR soon after it was introduced (1991 ish) at school. Prior to that i had already had the single vaccines that were offered back then (not sure what they were) I had previously had a mild case of rubella. When i was tested in pregnancy, i came back as immune to rubella and had assumed i was immune to measles and mumps too, just because i had the jab.
I was recently tested by occupational health, am training to be a SALT and it turns out although i am immune to rubella i am not to either to mumps or measles.
I am not to keen to have another MMR as i dont see why it will work when it didnt before. I am not sure if i will get another immunity test to see if this one works either.