The Contribution of Immunization Information System Data to Claims-Based Vaccine Administration Capture Over Time and Implications for Claims-Based COVID-19 Vaccine Studies

Background: Integrating COVID-19 vaccine data from United States (US) Immunization Information Systems (IIS) with claims data substantially increases the number of individuals identified as vaccinated, compared to claims data alone. However, it is unclear whether the contribution of IIS data to claims-based vaccine capture changes over time.

Objectives: To estimate the contribution of COVID-19 vaccine records from IIS to vaccine administration capture in claims data over time.

Methods: This cohort study included commercially insured individuals aged 6 months-64 years from 14 IIS jurisdictions from 01 Dec 2020 - 01 Dec 2022. Pharmacy and pre-adjudicated medical claims from the Optum database were linked to IIS vaccine records. The percent increase in vaccine capture by adding IIS data, calculated as a relative increase of vaccine records in the linked claims-IIS data compared to claims-based vaccine records alone, was evaluated in the overall population, by jurisdiction, and by month. Among claims-based vaccine records, vaccine administration setting (physician’s office, hospital, mass vaccination center, pharmacy, other) was evaluated by age and month.

Results: Of 4,332,982 individuals in the study, 1,579,274 (36%) had ≥1 vaccine record in claims data, 1,655,737 (38%) had ≥1 IIS vaccine record, and 2,240,403 (52%) had ≥1 vaccine record in either the claims or IIS data. Overall, IIS data increased the proportion of individuals with ≥1 vaccine record by 42%, an increase of 661,129 individuals. The contribution of IIS to vaccine capture in claims varied by jurisdiction, ranging from 29% to 77%, and by age, with a 6% increase among individuals ≤4 years and >40% increase for individuals ≥12 years. The contribution of IIS decreased over time, from a 280% increase in Dec 2020 to < 10% increase from Apr 2022 to Dec 2022. Among individuals with claims-based vaccine records, the proportion vaccinated at mass vaccination centers and hospitals decreased over time, whereas the proportion vaccinated at physician’s offices and pharmacies increased. Young children ( < 12 years) often received vaccines at physician’s offices, while older children and adults often received vaccines at pharmacies.

Conclusions: IIS data contributed substantially to the capture of vaccine records during the COVID-19 pandemic, especially in the early months and among older age groups. Over time, as more individuals received vaccinations at pharmacies and physician’s offices, the contribution of IIS data to COVID-19 vaccine capture diminished. These results are important to consider when conducting claims-based vaccine studies, given the study period and setting of vaccination affect the quality of data capture and necessity of using IIS vaccine records to supplement claims data.