State-Level Variations and Factors Associated with Adult Vaccination Coverage: A Multilevel Modeling Approach

Background Adult vaccination rates in the USA are generally low and fall short of public health goals. Objectives Our aim was to evaluate the effect of state-level characteristics on adult vaccination coverage in the USA. Methods This study was a cross-sectional, retrospective analysis of 2015–2017 Behavioral Risk Factor Surveillance System data, conducted from March to October 2019 and including seasonal influenza; pneumococcal; tetanus, diphtheria, and acellular pertussis (Tdap); and herpes zoster (HZ) vaccines. Multilevel logistic regression models examined interstate vaccination coverage variability and assessed the impact of state-level characteristics, with model-adjusted coverage estimated. Results Model-adjusted vaccination coverage varied by state, with 35.1–48.1% coverage for influenza (2017), 68.2–80.8% for pneumococcal (2017), 21.9–46.5% for Tdap (2016), and 30.5–50.9% for HZ (2017). Characteristics associated with vaccination included state-level insurance coverage, pharmacists’ vaccination authority, vaccination exemptions, and adult immunization information systems participation, as well as individual-level measures of income and education. After adjusting for these factors, substantial interstate heterogeneity remained. Conclusions Model-adjusted coverage was generally low and varied by state. A small number of state-level characteristics partially explained interstate coverage variability. This and future research assessing additional state characteristics may help determine policies most likely to increase adult vaccination.