This article summarises the various stages of the risk/benefit assessment of vaccination strategies. Establishing the awaited effectiveness of a vaccination strategy supposes to have an epidemiologic description of the disease to be prevented. The effectiveness of the vaccine strategy will be thus expressed in numbers of cases, hospitalizations or deaths avoided. The effectiveness can be direct, expressed as the reduction of the incidence of the infectious disease in the vaccinated subjects compared to unvaccinated subjects. It can also be indirect, the unvaccinated persons being protected by the suspension in circulation of the pathogenic agent, consecutive to the implementation of the vaccination campaign. The risks of vaccination related to the adverse effects detected during the clinical trials preceding marketing are well quantified, but other risks can occur after marketing: e.g., serious and unexpected adverse effects detected by vaccinovigilance systems, or risk of increase in the age of cases if the vaccination coverage is insufficient. The medico-economic evaluation forms a part of the risks/benefit assessment, by positioning the vaccine strategy comparatively with other interventions for health. Epidemiologic and vaccinovigilance informations must be updated very regularly, which underlines the need for having an operational and reliable real time monitoring system to accompany the vaccination strategies. Lastly, in the context of uncertainty which often accompanies the risks/benefit assessments, it is important that an adapted communication towards the public and the doctors is planned.