The prospects for many children born in developing countries to reach adulthood has been transformed over the last 30 years by the activities of the Expanded Programme of Immunization (EPI) established by the World Health Organization (WHO) in 1974. By 1990, about 80% of children had been vaccinated against six common childhood diseases. The advent of new technologies provided a strong stimulus to those involved in vaccine design, development and delivery, and offered the possibility of improving current vaccines, developing new vaccines and simplifying vaccination practices. This in turn led to the formation of the Children's Vaccine Initiative (CVI) in the early 1990s. The worldwide emergence of new diseases such as HIV/AIDS and the re-emergence of old diseases such as tuberculosis and cholera present additional challenges.