Talk to your pediatrician if your child gets exposed to mumps, even if you think he is up-to-date on his vaccines, as some kids need a third dose of the MMR vaccine during on-going mumps outbreaks.
Most outbreaks are started by someone who is unvaccinated, often after a trip out of the country, and the resulting outbreak will likely get many more unvaccinated than vaccinated folks sick.
Vaccines are safe, effective, and necessary. Vaccines work very well to protect us from the vaccine-preventable diseases that have now either been eliminated or are well controlled at much lower levels than they were at in the pre-vaccine era.
Although some vaccines require boosters, most vaccines provide long-lasting protection.