Vaccines for the world: major challenges for the future.

Vaccination is at a turning point. The global use of usual infant vaccines has led to a remarkable decrease in disease burden associated with measles, pertussis or diphtheria while rapid progress is being made towards eradication of poliomyelitis through mass immunization campaigns. However, new disease targets are now emerging and research priorities, at a global level, encompass the development of a series of new vaccines. Recent technological advances have made this possible but the challenge of universal immunization is likely to require particular approaches. For example, it will be essential, in the near future, to define optimal ways to use the capacity of the immune system to generate long-lasting protective responses against intra-cellular microorganisms, to develop vaccines efficient soon after birth and to devise new systems to simplify immunization. It will also be a real economic challenge to ensure that the new vaccines will become available for those who are at the highest risk, usually in the least developed countries.