Abstract
The immunization schedule is a dynamic public health tool that has incorporated different changes over the years influenced by the epidemiologic situation and the scientific evidence. The Immunization Advisory Committee [Ponencia de Programa y Registro de Vacunaciones], as the Interterritorial Council scientific and technical advisory body, carries out assessments of different programmes and vaccines and proposes changes that after approval will be introduced in the Regions schedule. This article is divided into two parts presenting the rationale followed to propose a new schedule for the immunization against diphtheria, tetanus, pertussis, hepatitis B and invasive disease by Haemophilus influenzae type b. This first part is focused in the reasoning to undertake the assessment, the review of the immunization policy and the impact of immunization in Spain, as well as a review of the immunization schedules in similar countries.