In the context of a pandemic, measuring the progress and impact of vaccination against a disease is essential for epidemiological surveillance. Vaccin Covid is the digital tool that enables the tracking of vaccinations, and VAC-SI is an information system derived from Vaccin Covid, serving as the database for COVID-19 vaccinations and monitoring indicators in the context of the pandemic. This article describes the implementation of the VAC-SI system in the midst of a health crisis, from the construction of the database with the various stakeholders involved to the production of indicators, including the use of the database by Santé publique France and its subsequent developments. In developing this new system, numerous technical challenges arose in response to various issues and needs, as well as changes in vaccination policy, which required constant adaptability and a high degree of responsiveness.