Those of us in our late 50s or older have probably never been vaccinated for measles, mumps, chicken pox, or other “childhood” diseases. Why? Because we had those diseases as children. In fact, anyone born before 1957 is automatically considered to have immunity to measles. Once vaccinations became readily available in 1963, the majority of parents who had experienced these diseases directly saw to it that their children were vaccinated to spare them the misery and possible serious complications that could result from those diseases. As a result, these diseases were virtually eradicated from the United States.
Many parents today have chosen not to vaccinate their children. Some have done so for religious reasons, some because of their personal beliefs, some because they are concerned about possible side effects from the vaccinations themselves, and a few for medical reasons. As a result, in many parts of the United States, the percentage of unvaccinated children has risen to the point where the percentage of those vaccinated is no longer sufficient to limit the spread of these diseases if and when they are re-introduced.