Implementation of a Novel Dormant State to Address Denominator Inflation in the Wisconsin Immunization Registry

Denominator inflation (DI) can burden long-standing immunization information systems (IIS), evident through a system having more client records than population estimates. DI underestimates IIS vaccination coverages compared to National Immunization Surveys (NIS) data. To mitigate DI, the Wisconsin Immunization Registry (WIR) implemented a dormant indicator in June 2020. Clients are presumed to have left the jurisdiction and are placed in the dormant state if they meet the following criteria: client age is at least 11 years old, no updates to the client record in at least 10 years, and the record has not been queried in the last five years. The querying component is a novel approach when compared to American Immunization Registry Association recommendations for the Patient Active/Inactive Status.

The study purpose was to quantify how incorporating the dormant state in an adolescent population assessment impacts Wisconsin's vaccination coverage rates compared to the NIS-Teen estimates. This study also addressed the population characteristics of adolescent dormant state and non-dormant state client records.

The study population included all Wisconsin adolescents, aged 13-18 years, and assessed vaccine uptake for Meningococcal ACWY , Tdap, HPV initiation, and HPV Complete. Vaccination coverage was assessed, with and without the dormant clients, and then compared to the NIS-Teen estimates. Descriptive statistics were assessed among dormant and non-dormant clients, including a regional variation assessment.

Initial results showed an increase in adolescent vaccination rates for all vaccines and series when excluding dormant clients and suggest a more accurate assessment in line with NIS-Teen estimates. Dormant clients had a higher proportion of unknown and missing data fields for race, sex, and ethnicity.

At this time, removing dormant client records is an effective strategy for reducing DI in WIR, with opportunities for further refinement.