It's reccomended that everyone get at least two doses of the MMR vaccine. It is not a perfect vaccine and there is a chance you would get mumps even after you had been vaccinated....more of a chance if your last vaccination had been many years ago, since the immunity does wane after time. However it is thought that if you were fully vaccinated and you managed to get the mumps, it would be a much less severe case. If you havent had the second dose, it would be a good idea to get it. A third dose is not reccomended nor does it offer any more immunity.