Immunization is one of the most cost-effective public health interventions, averting an estimated two to three million deaths every year. In these contexts, there is limited capacity to carry out basic health system activities, such as vaccination programmes, thus facilitating disease outbreaks. Supply chains become sporadic; cold chains lose viability; beneficiaries avoid dangerous travel to health centres; and human resources are dissipated, creating ever-larger pools of unvaccinated children that grow and jeopardize herd immunity. This document presents the issue, UNICEF's response and programmatic priorities, and the way forward.