Immunization reminders for providers in the electronic health record (EHR) are a type of clinical decision support (CDS) that can reduce missed immunization opportunities. One limitation of these reminders is that they generally depend only on data local to the EHR, which can be incomplete due to record scatter, leading to inaccurate alerts. An Immunization Information System (IIS), also known as an immunization registry, is a population-based system that collects immunization data primarily for children and adolescents from providers at a regional or state level.