Temporal changes in immunization information systems across U.S. states and jurisdictions, 2000-2024

Statewide immunization data are essential for monitoring vaccination trends and evaluating immunization program impact. In the United States, Immunization Information Systems (IIS) were established in the early 1990s to collect these data; however, operational, legal, and procedural details vary across states and over time. This study summarized differences in IIS characteristics, such as legal requirements and reporting procedures, across U.S. states and jurisdictions over time.

We compiled jurisdiction-level IIS regulatory data from published studies and Centers for Disease Control and Prevention (CDC) surveys conducted in 2000, 2012, 2018, and 2024 to compare changes in age-group coverage, provider reporting requirements, consent procedures, operating authority, and data-sharing regulations.

Between 2000 and 2024, legal frameworks and reporting practices for immunization registries expanded across U.S. states and jurisdictions. The number of states with laws or administrative rules authorizing immunization registries increased from 24 states in 2000 to all 50 states, Washington, D·C., five metropolitan areas, five U.S. territories, and three Freely Associated States in 2024. Over the same period, reporting requirements also became more widespread. The number of states and jurisdictions mandating providers to report immunization records increased from 12 (24% of 51) in 2000 to 54 (84% of 64) in 2024. Consent policies also changed over time. By 2024, most states and jurisdictions had adopted implicit consent for reporting children's immunization records (41/64; 64%), while a smaller proportion required explicit parental consent (7/64, 11%) or implemented mandatory participation without consent (14/64, 22%).

IIS infrastructure and reporting requirements have expanded across U.S. states and jurisdictions over the past two decades, while heterogeneity in consent policies and reporting practices persists. These temporal changes may need to be considered when interpreting IIS data, particularly in longitudinal and cross-jurisdictional analyses.