Vaccines are given for three reasons:
- For common diseases (like chickenpox, pertussis or pneumococcus), a choice not to get a vaccine is a choice to risk natural infection.
- Some diseases (like measles, mumps or Hib) still occur in the US at low levels. If immunization rates drop, even by as little as 10% or 15%, these diseases will come back
- While some diseases (like polio, rubella or diphtheria) have been either completely or virtually eliminated from the United States, they still occur in other parts of the world. Because international travel is common, these diseases are only a plane ride away from coming back into the United States.