Lessons learned and applied: what the 20th century vaccine experience can teach us about vaccines in the 21st century.

Most vaccines available in the United States have been incorporated into vaccination schedules for infants and young children, age groups particularly at risk of contracting infectious diseases. High universal vaccination coverage is responsible for substantially reducing or nearly eliminating many of the diseases that once killed thousands of children each year in the US. Despite the success of infant vaccinations, periods of low vaccination coverage and the limited immunogenicity and duration of protection of certain vaccines have resulted in sporadic outbreaks, allowing some diseases to spread in communities. These challenges suggest that expanded vaccination coverage to younger infants and adolescents, and more immunogenic vaccines, may be needed in some instances. This review focuses on the importance of infant immunization and explores the successes and challenges of current early childhood vaccination programs and how these lessons may be applied to other invasive diseases, such as meningococcal disease.