Vaccination Policies and Rates of Exemption from Immunization, 2005–2011

to the editor:

We computed the annual change in the rates of nonmedical exemptions from school immunization requirements and compared these rates between states that allow philosophical exemptions and states that allow only religious exemptions. We also compared states with respect to how difficult it is to obtain nonmedical exemptions because of certain administrative procedures. We used data compiled by the Centers for Disease Control and Prevention (CDC) for school years 2005–2006 through 2010–2011.¹ State-specific categories of difficulty in obtaining exemptions were based on several factors: whether completion of a standardized form was permissible, as opposed to a letter from a parent; where the parent obtained the form (i.e., school vs. health department); whether the form had to be notarized; and whether a letter from a parent, if required, needed to be worded a specific way, resulting in extra effort on the part of the parent.

Over the study period, unadjusted rates for nonmedical exemptions in states that allowed philosophical exemptions were 2.54 times as high as rates in states that allowed only religious exemptions (incidence rate ratio [IRR], 2.54; 95% confidence interval [CI], 1.68 to 3.83) (see Table S1 in the Supplementary Appendix, available with the full text of this letter at NEJM.org). Although the absolute rates were higher in states that allowed philosophical exemptions, the average annual rate increase among states that allowed only religious exemptions (IRR for change per year, 1.20; 95% CI, 1.11 to 1.30) was higher than the rate in states that allowed philosophical exemptions (IRR for change per year, 1.10; 95% CI, 1.05 to 1.14).

During the study period, unadjusted rates of nonmedical exemptions in states with easy exemption policies were 2.31 times as high as rates in states with difficult exemption policies (IRR, 2.31; 95% CI, 1.39 to 3.85). By 2011, the nonmedical exemption rate in states with easy exemption criteria increased to 3.3%, an average annual increase of 13% (IRR for change per year, 1.13; 95% CI, 1.05 to 1.21) (Fig. 1, and Table S1 in the Supplementary Appendix). In contrast, nonmedical exemption rates in states with difficult exemption criteria increased by 8% annually to 1.3% in 2011 (IRR for change per year, 1.08; 95% CI, 1.02 to 1.14). In states with exemption criteria of medium difficulty, rates increased by 18% annually to 2.0% in 2011 (IRR for change per year, 1.18; 95% CI, 1.10 to 1.26). For all analyses, adjusted results were qualitatively similar to unadjusted results (Table S1 in the Supplementary Appendix).

Figure 1. Rates of Nonmedical Exemptions from School Immunization, According to Type of Exemption and Ease of Obtaining One, 2006–2011.

Overall mean rates of nonmedical exemptions per year for 48 states and the District of Columbia (excluding Mississippi and West Virginia, which do not allow nonmedical exemptions), as well as the rates for the types of exemptions allowed (religious reasons only and philosophical reasons permitted), are shown for the years 2006 through 2011 (top row of graphs). Mean rates of nonmedical exemptions per year according to the level of difficulty (easy, medium, or difficult, as modified from the criteria described by Rota et al.²) of the exemption policies are also shown (bottom row of graphs). I bars represent 95% confidence intervals.

In an earlier analysis of data from 1991 through 2004, we found an increase in exemption rates only in states with philosophical exemptions and in states with easy exemption procedures. Even in these states the average rate of increase was lower than that found during the current study period.³ Our results show that nonmedical exemptions have continued to increase, and the rate of increase has accelerated.