Background: Kindergarten-entry vaccination requirements have played an important role in controlling vaccine-preventable diseases in the United States. Forty-eight states and the District of Colombia offer nonmedical exemptions to vaccines, ranging in stringency.
Methods: We analyzed state-level exemption data from 2011 to 2012 through 2015 to 2016 school years. States were categorized by exemption ease and type of exemption allowed. We calculated nonmedical exemption rates for each year in the sample and stratified by exemption ease, type, and 2 trend categories: 2011-12 through 2012-13 and 2013-14 through 2015-16 school years. Using generalized estimating equations, we created regression models estimating (1) the average annual change in nonmedical exemption rates and (2) relative differences in rates by state classification.
Results: The nonmedical exemption rate was higher during the 2013-2014 through 2015-2016 period (2.25%) compared to 2011-2012 through 2012-2013 (1.75%); more importantly, the average annual change in the latter period plateaued. The nonmedical exemption rate in states allowing philosophical and religious exemptions was 2.41 times as high as in states allowing only religious exemptions (incidence rate ratio = 2.41; 95% confidence interval, 1.71-3.41).
Conclusions: There was an increase in nonmedical exemption rates through the 2012-2013 school year; however, rates stabilized through the 2015-2016 school year, showing an important shift in trend.
Keywords: epidemiology; vaccination; vaccine exemption; vaccine hesitancy.