Vaccinology in the third millennium: scientific and social challenges.

The epidemiology of deaths due to vaccine-preventable diseases has been significantly and positively altered through the use of vaccines. Despite this, significant challenges remain in vaccine development and use in the third millennium. Both new (Ebola, Chikungunya, Zika, and West Nile) and re-emerging diseases (measles, mumps, and influenza) require the development of new or next-generation vaccines. The global aging of the population, and accumulating numbers of immunocompromised persons, will require new vaccine and adjuvant development to protect large segments of the population. After vaccine development, significant challenges remain globally in the cost and efficient use and acceptance of vaccines by the public. This article raises issues in these two areas and suggests a way forward that will benefit current and future generations.