Immunization information systems (IISs) are accessible sources of immunization data. We validated immunization information from a local IIS against provider records and assessed the system's utility in evaluating vaccine effectiveness against rotavirus disease using a case-control study. Among the 91% of case and control patients with immunization records, 49% were in the IIS, and 97% had a provider record. Good agreement was observed across record sources (k=0.65). Vaccine effectiveness (VE) was 82% using IIS data compared to 82-88% using provider data. Controls identified through the IIS provided VE estimates similar to hospital control patients. IISs could represent a valuable source of data for effectiveness evaluations.
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