By the time they are six years old, most kids in the United States have received 49 doses of 14 different vaccines. This is the standard immunization schedule recommended by the Centers for Disease Control, as well as many pediatricians. But, how did we get to this point? When were the first vaccines developed? Who oversees the research, development, efficacy and safety of vaccinations in the United States? And why have vaccinations become such a controversial topic?