Data and information are vital to the daily work of public health practitioners, the data they use come from a variety of sources. Examples of these data sources are: vital statistics databases, surveillance data, morbidity data, and Immunization Information Systems (IISs). These IISs are of particular interest because of their near ubiquity in the Unites States, their importance for public health practice, and their most basic function of providing cross-organizational access to immunization-related clinical data for both public and private health care providers. As the infrastructure to connect electronic health record (EHR) systems and public health systems expands, public health practitioners will have the opportunity to access an unprecedented volume of patient level clinical information. The flood of information and data will have the greatest public health impact if understood and organized within the framework of public health practitioners' data and information needs. This work uses qualitative methods to identify and understand the information needs of public health practitioners related to immunization work and the data and information source characteristics that are important in meeting those needs. The study also uses quantitative methods to describe two important data source characteristics in Washington's IIS: timeliness and data element completeness. Results point to three main types of information needs of public health practitioners: individual level, population level and context-specific information (vaccine-specific information in this case). These results further the understanding of information work in public health across local and state public health organizations. The results also provide solid evidence related to the effect of different methods of data transfer on data quality. In addition, synthesis of the qualitative and quantitative components of this work provides evidence to support a set of recommendations presented to state level stakeholders in Washington. This research will help inform the development of technical and non-technical infrastructure to support data sharing between healthcare providers, health information exchanges, and public health organizations.