Recall is performed centrally by public health departments for all children in need of immunizations in a geographic area.

Reminder/Recall is performed by individual private practices for their patients who appear in need of immunizations.

All practices in these counties will receive training on practice-based R/R using the Colorado Immunization Information System (CIIS or immunization registry). Practices will receive a recommended schedule for conducting recall in 19-35 month children and educational materials to use within their practices to promote compliance with the infant vaccination schedule. Individual practices will make their own decisions about the extent to which they follow the recommendations and implement recall within their practice. Although the study team will not provide them with any additional interventions, we will track any other interventions they independently do (websites, newsletters, telephone informational systems) in order to assess the effect of these additional interventions.

The primary outcome measures will be: 1) change in up-to-date rates from baseline levels 6 months after the intervention (T-1) for 19-35 month olds in population-based compared to practice-based intervention counties and 2) percent of children who were not up-to-date prior to recall (T-0) who received any additional new vaccine in each type of intervention county.