[Vaccines: history and stories between reality and imagination].

Vaccinations and the controversy around them always go in parallel. We identified four categories blending in various amounts of truth and imagination: history, myths, shams and frauds. Over the years, they have alternated and sometimes transformed into one another. This sharp separation into categories is certainly academic and forced. In fact, the line between these aspects is not clear enough to allow a rigid and well-defined division. Our work starts from the category containing the most truthfulness: history, and goes on to analyze two categories that add fantasy to facts: myths and shams (or better, "old wives' tales"). The history deals with the topics of variolation and the first anti-vaccine activists' disputes. Myths that arose around immunization include immune overload, homeoprophylaxis, and excessive hygiene. In this context, immunization itself risked becoming a myth, being considered not amenable to improvements. In the category of old wives' tales we find rumors about the presence in the vaccines of considerable quantities of supposedly toxic components such as aluminum, squalene, Thimerosal and nanoparticles, as well as the existence of secret techniques of vaccine preparation that involve unethical procedures. The last category, fraud, is the poorest in both truth and fantasy but it is still hard to confront. The most famous fraud is the supposed link between vaccines and autism. In this frame, disinformation is certainly a fertile substrate for the emergence both of elements close to reality and of very imaginative ones. Vaccine hesitancy is believed to be responsible for decreasing vaccine coverage and increasing the risk of vaccine-preventable disease outbreaks and epidemics. The role of communication in immunization is essential to its success, especially taking into account the deep transformations the world of information is going through. The great multitude of voices seem to carry the same weight, but it is not so in science. Web searches are influenced by the filter bubble phenomenon, which contributes to the radicalization of people's opinion through cognitive isolation. A new, more effective strategy of communication is required in order to regain the trust of populations in immunization in a context characterized by the presence of groups impervious to scientific evidence.