This study evaluates the impact of the Global Alliance for Vaccines and Immunization (GAVI) on children's health outcomes in developing countries. Using a difference-in-differences identification strategy, we find that GAVI has reduced neonatal, infant and under-five mortality rates. The impact of GAVI on children's health outcomes is larger in countries with lower per capita income. Our findings underscore the relevance of health interventions in improving children's health outcomes in developing economies.