New England Journal of Medicine
September 20, 2012  Vol. 367 No. 12
http://content.nejm.org/current.shtml

Correspondence
Vaccination Policies and Rates of Exemption from Immunization, 2005–2011
N Engl J Med 2012; 367:1170-1171September 20, 2012

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

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.

Saad B. Omer, M.B., B.S., Ph.D.; Jennifer L. Richards, M.P.H.; Michelle Ward, A.B.; Robert A. Bednarczyk, Ph.D.; Rollins School of Public Health, Emory University, Atlanta, GA