Vaccines have contributed to a significant reduction in many childhood infectious diseases, such as diphtheria, measles, and Haemophilus influenzae type b (Hib). Some infectious diseases, such as polio and smallpox, have been eliminated in the United States due to effective vaccines. It is now rare for children in the United States to experience the devastating and often deadly effects of these diseases that were once common in the United States and other countries with high vaccination coverage. The vast majority of vaccines are given to healthy babies, children and adults; therefore, it is critical that vaccines be demonstrated to be safe and effective. Ensuring the safety and effectiveness of vaccines is one of the Food and Drug Administration’s (FDA) top priorities. The Center for Biologics Evaluation and Research (CBER) is the center within FDA that has regulatory oversight of vaccines in the United States assuring the availability of safe and effective vaccines.