At the request of the Île-de-France Regional Health Agency (ARS), the Interregional Epidemiology Unit (Cire) and the Regional Health Observatory (ORS) conducted an assessment of the available data on vaccine-preventable diseases, focusing on vaccination among children and adolescents. To date, the primary sources of information remain children’s health certificates. However, the low participation of physicians and families in this system for the 9-month and 24-month certificates raises questions about the representativeness of the data. This bias is compounded by the difficulties encountered by certain General Councils in entering the information received. The triennial cycle of surveys on the health of children and adolescents allows for estimating vaccination coverage among children in the Île-de-France region aged approximately 6, 11, and 15 years. A limitation of these surveys is the time lag between data collection and availability, which remains somewhat long. Other data sources allow for monitoring vaccination in the region: vaccine sales to pharmacies and local authorities, specific surveys, and vaccination promotion campaigns in schools. Furthermore, the use of data from the National Inter-Regime Health Insurance Information System (SNIIRAM) is currently under consideration. The data presented highlight certain specific challenges: - Insufficient Bacillus Calmette-Guérin (BCG) vaccination coverage given the risk in the Île-de-France region, though it is satisfactory when targeting the populations most at risk. - Shortcomings regarding measles-mumps-rubella (MMR) vaccination as well as hepatitis B vaccination. Overall, the system for assessing vaccination coverage in Île-de-France needs to be strengthened. To date, no database possesses the necessary characteristics to enable detailed regional or population-based analysis capable of identifying potential pockets of under-vaccination. Furthermore, vaccination coverage among young people in the Île-de-France region around the age of 15 remains insufficiently documented. Proposals to improve this system are presented in this report.