  Background: Globally, influenza is a major cause of morbidity,
hospitalization and mortality. Influenza vaccination has shown substantial
protective effectiveness in the United States. We investigated state-level
patterns of coverage rates of seasonal and pandemic influenza vaccination,
among the overall population in the U.S. and specifically among children and
the elderly, from 2009/10 to 2014/15, and associations with ecological factors.
Methods and Findings: We obtained state-level influenza vaccination coverage
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 mixed-model regression 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. We found that
health-care access is positively and significantly associated with mean
influenza vaccination coverage rates across all populations and models. We also
found that prevalence of asthma in adults are negatively and significantly
associated with mean influenza vaccination coverage rates in the elderly
populations. Conclusions: Health-care access has a robust, positive association
with state-level vaccination rates across different populations. This
highlights a potential population-level advantage of expanding health-care
access.
