Measuring immunization coverage.

OBJECTIVE: Information about immunization coverage comes from five major sources: the National Immunization Survey, the National Health Interview Survey, retrospective school-entry surveys, the Health Plan Employer Data and Information Set (HEDIS) measures reported by managed care plans, and assessments performed on clinics and private practices. In this article, we describe the methodology of the major surveys, discuss technical and policy issues in measuring immunization coverage, and identify issues that must be addressed to harmonize immunization rates calculated from different sources. METHODS AND TOPICS: We describe the (1) design and methodology of the five major sources of immunization coverage assessments, (2) issues and controversies in measuring immunization coverage, and (3) preliminary efforts to harmonize calculation of immunization coverage. Technical and policy issues involve dose and interval requirements, which vaccines are included in the series-completion calculations, and who is excluded from each method of calculation.
CONCLUSIONS: The purpose of measuring up-to-date immunization coverage determines the way that it is measured. The tension between measuring immunization coverage to monitor population protection against disease and measuring immunization coverage to determine how well the health care delivery system is working leads to different ways of selecting a sample and reporting coverage. These differences create confusion for the public policymakers who try to identify problems and to set priorities for immunization efforts. Although some unavoidable differences may occur because of differences in purpose of the measurement, greater harmonization is possible.