Being vaccinated doesn't automatically assume you will never get it! It is usually your body being able to deal with the disease much more easily and symptoms are not as full on and or painful...sometimes even life threatening!
I was vaccinated as a child and never caught chicken pox till I was 18 and felt fine, the doctor told me that as an adult and not being vaccinated I would of been quite sick...
Just do what sits right with you and your beliefs.