BACKGROUND:
Immunization records entered into the California Medicaid (Medi-Cal) billing system are a potential large source of data for the state's immunization registries. California has nine state-funded immunization registries in varying phases of development.

OBJECTIVE:
We investigated the feasibility of using the Medi-Cal billing system as a data source for the state immunization registries through a pilot merge of data.

METHOD:
We collected immunization and demographic data from July 1 2001 to January 1 2004 in the Medi-Cal billing database from children ages 0-6 years residing in four California Counties. We compared the Medi-Cal billing data to immunization registry data from the same time period using SAS software and SQL. We assessed the completeness of each dataset and the feasibility of merging them.

RESULT:
In process.

CONCLUSION:
In process.

LEARNING OBJECTIVES:
We address issues of data standards, data completeness, and strategies for merging records which lack a unique identifier.