BACKGROUND: Previous studies on adult vaccination coverage found inter-state variability that persists after adjusting for individual demographic factors. Assessing the impact of state-level factors may help improve uptake strategies. This study aimed to:
• Update previous estimates of state-level, model-adjusted coverage rates for influenza; pneumococcal; tetanus, diphtheria, and acellular pertussis (Tdap); and herpes zoster (HZ) vaccines (individually and in compliance with all age-appropriate recommended vaccinations)
• Evaluate effects of individual and state-level factors on adult vaccination coverage using a multilevel modeling framework.
METHODS: Behavioral Risk Factor Surveillance System (BRFSS) survey data (2015-2017) were retrospectively analyzed. Multivariable logistic regression models estimated state vaccination coverage and compliance using predicted marginal proportions. BRFSS data were then combined with external state-level data to estimate multilevel models evaluating effects of state-level factors on coverage. Weighted odds ratios and measures of cluster variation were estimated.
RESULTS: Adult vaccination coverage and compliance varied by state, even after adjusting for individual characteristics, with coverage ranging as follows:
• Influenza (2017): 35.1-48.1%
• Pneumococcal (2017): 68.2-80.8%
• Tdap (2016): 21.9-46.5%
• HZ (2017): 30.5-50.9%
Few state-level variables were retained in final multilevel models, and measures of cluster variation suggested substantial residual variation unexplained by individual and state-level variables. Key state-level variables positively associated with vaccination included health insurance coverage rates (influenza/HZ), pharmacists’ vaccination authority (HZ), presence of childhood vaccination exemptions (pneumococcal/Tdap), and adult immunization information system participation (Tdap/HZ).
CONCLUSION: Adult vaccination coverage and compliance continue to show substantial variation by state even after adjusting for individual and state-level characteristics associated with vaccination. Further research is needed to assess additional state or local factors impacting vaccination disparities.
