This case study appears in: Mays C, Laborie L, Griset P (eds) (2022) Inventing a shared science diplomacy for Europe: Interdisciplinary case studies to think with history. Vaccination has become a global concern as intergovernmental actors such as the World Health Organization (WHO) have reinforced their efforts to foster transnational collaboration on vaccine-preventable diseases. As the ongoing COVID-19 pandemic has once more made visible, such global efforts are challenged by the contingencies of national immunization programs. Divergences between the global and the local, we show, are sidelined and resolved diplomatically in WHO data practices. We conceptualize data practices as a form of health diplomacy and their infrastructures as constitutive of global vaccination governance and diplomacy. Based on interviews with global health actors and an extensive documentary analysis, we show how datafication is both an effect of and a means for health diplomacy. We further discuss some of the political implications of datafication, such as rendering political problems into technical ones.