The Contribution of Immunization Information System Data to Claims-Based Capture of Vaccines Used to Prevent Mpox and Implications for Claims-Based Mpox Surveillance

Background: Vaccine records from United States (US) Immunization Information Systems (IIS) substantially increased the number of individuals identified as vaccinated for COVID-19 compared to claims data alone. Given vaccines used to prevent mpox were sent from the strategic national stockpile and often administered by health departments, IIS data are expected to increase capture of vaccines used to prevent mpox, but the level of contribution of IIS data to claims data is unknown.

Objectives: To estimate the contribution of mpox vaccine records from IIS data to vaccine capture in a claims database.

Methods: Commercially insured individuals aged 6 months-64 years from 14 US jurisdictions between 01 June 2022 and 01 Nov 2022 were included. Pharmacy and pre-adjudicated medical claims from the Optum database were linked to mpox vaccine records from IIS. The contribution of IIS to claims-based vaccine administration records was estimated as a percent increase, calculated as the count of individuals with at least one vaccine record in the linked claims-IIS data compared to the count of individuals with at least one vaccine record in claims data alone. The percent increase in vaccine capture with the addition of IIS data was evaluated by month in 2 jurisdictions with complete IIS data during the study period.

Results: Of 4,332,982 individuals in the study, 3,325 (0.1%) had ≥1 mpox vaccine record in claims data, 3,529 (0.1%) had ≥1 vaccine record in IIS, and 6,589 (0.2%) had ≥1 vaccine record in claims or IIS data. Overall, IIS data increased the proportion of individuals with ≥1 mpox vaccine record by 98%, but this is likely an under-estimate due to data lag from some IIS. Two jurisdictions accounted for >90% of mpox IIS vaccine records, including 2,930 from Jurisdiction A and 295 from Jurisdiction B. In these two jurisdictions, IIS data increased the proportion of individuals with ≥1 vaccine record by >800%, an increase of 2,733 and 272 individuals in Jurisdictions A and B, respectively, with ≥1 mpox vaccine record in the linked claims-IIS data compared to claims data alone. In both jurisdictions, the contribution of IIS data to claims-based vaccine capture decreased each month but remained over 100% in Nov 2022.

Conclusions: The supplementation of IIS data to claims-based capture of vaccines used to prevent mpox doubled the number of individuals with ≥1 vaccine record during the mpox outbreak in 14 IIS jurisdictions from June-Nov 2022. The overall observed percent increase may be artificially low due to data lags in IIS repositories, which ongoing work will address. Increases were higher in jurisdictions with more complete IIS data. It is recommended that future studies of mpox vaccines use IIS data to supplement claims-based vaccine records for more complete data capture.