A systematic evaluation of different methods for calculating adolescent vaccination levels using immunization...

Area of Science:

• Public Health
• Epidemiology
• Biostatistics

Background:

• Immunization Information Systems (IISs) are crucial for monitoring vaccination coverage.
• Population mobility can introduce bias in IIS-derived coverage estimates.
• Accurate estimation of the vaccine-eligible population is essential for reliable public health assessments.

Purpose of the Study:

• To evaluate alternative methods for estimating the vaccine-eligible population for adolescent immunization coverage calculations using a statewide IIS.
• To assess the impact of different denominator estimation methods on state- and county-level immunization coverage rates.

Main Methods:

• Retrospective analysis of the Michigan State Care Improvement Registry (MCIR) for adolescents aged 11-18 years.
• Comparison of four denominator calculation methods: (1) all MCIR records, (2) excluding out-of-state residents, (3) excluding records with no recent activity, and (4) U.S. Census data.
• Estimation of state- and county-specific coverage for four adolescent vaccines.

Main Results:

• A 20% difference in estimated vaccination coverage was observed between the most inclusive and restrictive denominator methods.
• Variability in coverage estimates ranged from 2%-11% at the state level and up to 21% at the county level.
• Higher coverage vaccines and smaller counties exhibited greater absolute variation in estimates.

Conclusions:

• Denominator calculation methods significantly impact estimated adolescent immunization rates, particularly at the county level.
• State-level aggregation can mask substantial county-level variations.
• Further research is required to determine the optimal method for estimating vaccine coverage using IIS data.