Last month, the World Health Organization certified India and Southeast Asia as being polio-free, an extraordinary achievement given that the polio vaccine was declared safe and effective only 59 years ago. Vaccines are one of the safest and most cost-effective medical interventions in history. By immunizing infants, children, and teenagers, vaccines protect the entire community. Nevertheless, there is a surge of outbreaks in vaccine-preventable diseases in the United States. What research is needed to reverse this trend?