Characterization of Heterogeneity in Childhood Immunization Coverage in Central Florida Using Immunization Registry Data.

Despite high vaccine coverage in the United States in general, and in the State of Florida specifically, some children miss scheduled vaccines due to health system failures or vaccine refusal by their parents. Recent experiences with outbreaks in the United States suggest that geographic clustering of un(der)vaccinated populations represent a threat to the elimination status of some vaccine-preventable diseases. Immunization registries continue to expand and play an important role in efforts to track vaccine coverage and use. Using nearly 700,000 de-identified immunization records from the Florida Department of Health immunization information system (Florida SHOTS™) for children born during 2003-2014, we explored heterogeneity and potential clustering of un(der)vaccinated children in six counties in central Florida-Brevard, Lake, Orange, Oseola, Polk, and Seminole-that represent a high-risk area for importation due to family tourist attractions in the area. By zip code, we mapped the population density, the percent of children with religious exemptions, the percent of children on track or overdue for each vaccine series without and with exemptions, and the numbers of children with no recorded dose of each vaccine. Overall, we found some heterogeneity in coverage among the counties and zip codes, but relatively consistent and high coverage. We found that some children with an exemption in the system received the vaccines we analyzed, but exemption represents a clear risk factor for un(der)immunization. We identified many challenges associated with using immunization registry data for spatial analysis and potential opportunities to improve registries to better support future analyses.