Vaccination is one of the most successful tools for controling infectious diseases. Although it is generally perceived as the ”golden solution”, it has been shown recently that the extensive use of vaccines may lead to undesirable effects (e.g. poliomyelitis epidemics due to vaccine-derived viruses) or the resurgence of a disease and its clinical characteristics as well as the development of new biological diagnosis (e.g. re-emergence of whooping cough after 40 years of vaccination). In the documented cases, epidemiological studies clearly indicate that extensive vaccinations can induce modifications of the pathogens over time, the emergence of new pathogens due to changes in the ecosystems, or change in the transmission of the disease. Therefore, to optimise the benefits of immunization programs and prevent new global adverse effects of vaccines (and the subsequent detrimental impact in the general public), the consequences of extensive vaccinations on the pathogen, ecosystem and/or human host populations remain to be evaluated.
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