Understanding Over-immunization in North Dakota's Adult Population

Abstract

Context: Over-immunization, or administration of excess doses of vaccine, is an understudied topic in immunization. Adult over-immunization is particularly understudied, so building a basic understanding of the sources and scope of over-immunization is necessary to direct action. Objective: The aim of this evaluation was to quantify the extent of over-immunization in North Dakota's adult population from 2016 to 2021. Design: Records for all pneumococcal, zoster, and influenza vaccines administered to adults in North Dakota were extracted from the North Dakota Immunization Information System (NDIIS) from January 1, 2016, through December 31, 2021. The NDIIS is a state-wide immunization registry that captures all childhood and most adult immunizations. Setting: North Dakota. Participants: North Dakotan adults 19 years or older. Main Outcome Measure: The number and percentage of adults identified as over-immunized as well as the number and percentage of doses identified as an extra dose. Results: Frequency of over-immunization was less than 3% for all vaccines over the 6-year period assessed. Pharmacies and private practices were the most common sources of over-immunization of adults. Conclusions: These data show that over-immunization is still an issue in North Dakota, although the percentage of the adult population impacted is low. Reducing over-immunization is worth pursuing but should be balanced with the importance of improving low immunization coverage rates in the state. Improving utilization of the NDIIS by adult providers can help prevent over-immunization and under-immunization alike.