To summarize, vaccines are regulated in the United States as biologics by CBER and must meet requirements for safety, purity, and potency (efficacy). Although general requirements exist for safety, purity, and potency, specific standards for each vaccine are agreed to by the manufacturer and CBER. The final standards for any vaccine are relevant to the technology used to produce the vaccine. Vaccine efficacy is demonstrated through conducting one or more Phase III trials. A single, definitive, well-controlled, double-blind, placebo-controlled Phase III trial often provides sufficient efficacy data for licensing a vaccine. Pivotal efficacy data may be derived from U.S. or outside the U.S. studies. Bridging studies may be required to link the efficacy data to the intended marketing target population. In the United States, approval for conducting clinical trials is obtained from the FDA through the mechanism of the IND application. Marketing approval is obtained through the mechanism of the PLA and ELA. Postmarketing Phase IV clinical trials are generally requested to develop large-scale field data for safety. Timely communication with the FDA throughout the development and approval process is the most efficient mechanism for meeting all regulatory requirements in the shortest possible time.