Patterns of influenza vaccination coverage in the United States from 2009 to 2015.

BACKGROUND Globally, influenza is a major cause of morbidity, hospitalization and mortality. Influenza vaccination has shown substantial protective effectiveness in the United States. METHODS We investigated state-level patterns of coverage rates of seasonal and pandemic influenza vaccination, among the overall population (six months or older) in the U.S. and specifically among children (aged between 6 months and 17 years) and the elderly (aged 65 years or older), from 2009/10 to 2014/15, and associations with ecological factors. We obtained state-level influenza vaccination rates from national surveys, and state-level socio-demographic and health data from a variety of sources. We employed a retrospective ecological study design, and used both linear models and linear mixed-effect models to determine the levels of ecological association of the state-level vaccinations rates with these factors, both with and without region as a factor for the three populations. RESULTS AND CONCLUSIONS Health-care access has a robust, positive association with state-level vaccination rates across all populations and models. This highlights a potential population-level advantage of expanding health-care access. We also found that prevalence of asthma in adults is negatively associated with mean influenza vaccination rates in the elderly populations.