Assessment of immunization registry databases as supplemental sources of data to improve ascertainment of vaccination coverage estimates in the National Immunization Survey

Objective: To evaluate the use of immunization registry data to supplement missing or incomplete vaccination data reported by immunization providers (referred to as "providers" hereafter) in the National Immunization Survey. Design: Cross-sectional, random-digit-dialing, telephone survey to measure vaccination coverage among children aged 19 to 35 months in the United States. Setting: Four sites with mature (with > 67% of provider participation in the area) immunization registries. Participants: Of the 639 children with complete household interviews, interviewers had consent from the respondents for 569 (89.0%) children to contact their providers and for 556 (87.0%) children to contact both providers and registries. Main Outcome Measures: Percentages of children up-to-date for vaccines based on data from providers, registries, and both sources combined. Results: According to provider-reported data, weighted estimates of coverage for the recommended childhood vaccine series 4:3:1:3 at the 4 sites were 65.6%, 78.8%, 81.6%, and 77.0%. According to registry data, these coverage rates were consistently lower: 31.7% (P <.05), 65.4%, 71.9%, and 61.8%, respectively. When all unique vaccine doses were combined from both sources, the pooled 4: 3: 1: 3 coverage rates increased to 72.0%, 92.0%, 88.7%, and 80.2%, respectively. The quality and completeness of vaccination histories from the registries were inconsistent and varied by sites. Conclusions: Vaccination coverage estimates were the lowest when only registry-reported data were used and were the highest when provider- and registry-reported histories were combined. Although registries enrolled and matched more children, vaccination histories were missing, incomplete, and inconsistent. The quality and completeness of the registry data must be improved and must be comparable across all states before further consideration may be given to supplement or replace the provider-reported National Immunization Survey data.