The regional immunization registry as a public health tool for improving clinical practice and guiding immunization delivery policy.

Objectives: We assessed the distribution of immunization records among 3 health care delivery sectors and the impact of a regional immunization registry on "up to date" rates.

Methods: Immunization registry records in 2 regions were categorized as having originated in private practices, community health centers, or public health clinics. "Up to date" rates were calculated after we sequentially added immunization records from the 3 sectors.

Results: The percentage of children with immunizations documented in multiple sectors increased with age from 7 to 24 months, and children who were seen in multiple sectors were more likely to be up to date. There were relative increases in "up to date" rates of 50% for children aged 24 months.

Conclusions: The regional immunization registry is a powerful public health tool for increasing documented "up to date" rates and providing insights into patterns of immunization delivery.