Background: Immunization information systems (IIS) are confidential, population-based computerized databases that record vaccination doses administered to persons residing within a given geopolitical area. They play a pivotal role in achieving equitable and high vaccine uptake. In the United States (US), they are implemented and managed at the state and local level, creating variability in IIS policies. Methods: We conducted a legal assessment of relevant IIS statutes and administrative codes across all 50 states, the District of Columbia, Philadelphia, and New York City. Where relevant, laws were cross-checked or supplemented with state and local health department resources. Comparisons to previous legal studies were used to evaluate trends in IIS laws over time. Results: The compilation of these laws provides an updated overview of the diverse inter- and intra-state policies within the US that govern the capabilities and implementation of IIS. The findings of this study show that while progress has been made in improving the policies to enable and enhance IIS, gaps in IIS data collection, limited interoperability with local and national health information systems, and inconsistent access to IIS to view or utilize records, limits the full potential of IIS. Conclusions: Findings from this study help shine a light on the evolution of IIS policy over the last two decades, serve as a comprehensive benchmark for future analyses, and may help policy stakeholders who are exploring amending jurisdictional IIS laws.

The COVID-19 pandemic has focused attention on the use of immunization information systems (IIS) to record and consolidate immunization records from a variety of sources to generate comprehensive patient immunization histories. Operationalization of IIS in the United States is decentralized, and as such, there are over 60 different IIS with wide variations in enabling policies and functionalities. As such, the policies that inform the development and operation of those sub-national IIS exist at the state and sometimes city levels. A targeted literature review was conducted to identify IIS policies and functionalities and assess their impact. The authors identified articles published from 2012 to 2022 that discussed or evaluated IIS policies and functionalities and screened titles, abstracts, and full text for inclusion. When selected for inclusion, authors extracted IIS policy/functionality characteristics and qualitative or quantitative outcomes of their implementation, where applicable. The search terms yielded 86 articles, of which 39 were included in the analysis. The articles were heterogeneous with respect to study design, interventions, outcomes, and effect measures. Out of the 17 IIS policies and functional components identified in the targeted literature review, the most commonly evaluated were provider-based patient reminder/recall, IIS-based centralized reminder/recall, and clinical decision support. Patient reminder/recall had the most published research and was associated with increased vaccination rates and vaccine knowledge. Despite the lack of quantitative evidence, there is a consensus that immunization data interoperability is critical to supporting IIS data quality, access, and exchange. Significant evidence gaps remain about the effectiveness of IIS functionalities and policies. Future research should evaluate the impact of policies and functionalities to guide improved utilization of IIS, increase national interoperability and standardization, and ultimately improve vaccination coverage and population health.