Despite a well documented efficacy and a generally good adhesion of a large majority of the lay population and health care professionals as well, immunization is still the object of controversies. It affects several vaccines against hepatitis B, influenza, BCG, pertussis and measles. In most cases, polemics on vaccination result from a temporal association between a vaccination and the revelation of a serious disease, when the immunization is performed at the peak of incidence of the disease. Controversies can also be initiated by scientific publications, even though these are often biased, by a misinterpretation or the absence of official positions from the health care authorities, or by justice decisions, whose criteria differ from the scientists' ones and are therefore difficult to understand for the lay public. Furthermore, the scientific demonstration of the exclusion of a risk is difficult to obtain. In the past, it appeared to be very difficult to stop controversies. Improving the communication is the main issue, towards lay public as well as health care professionals. This implies to learn how to better use the media, to motivate and educate professionals who administer vaccine, and anticipate the eventuality of a temporal relationship between vaccination and occurrence of a serious disease by an improved management of the pharmacovigilance system.