摘要：We summarized studies describing the prevalence of, trends in, and correlates of nonmedical exemptions from school vaccination mandates and the association of these policies with the incidence of vaccine-preventable disease. We searched 4 electronic databases for empirical studies published from 1997 to 2013 to capture exemption dynamics and qualitatively abstracted and synthesized the results. Findings from 42 studies suggest that exemption rates are increasing and occur in clusters; most exemptors questioned vaccine safety, although some exempted out of convenience. Easier state-level exemption procedures increase exemption rates and both individual and community disease risk. State laws influence exemption rates, but policy implementation, exemptors’ vaccination status, and underlying mechanisms of geographical clustering need to be examined further to tailor specific interventions. Childhood vaccinations are one of the most significant public health interventions of all time. They reduce the risk of contracting dangerous vaccine-preventable childhood diseases on the individual level and, when immunization coverage is high enough, confer herd immunity at the population level for those diseases that are contagious. 1,2 Recognizing the public health importance of the childhood immunization schedule, all 50 US states require parents to provide documentation of immunization for admission to school and day care, a mandate that has been crucial for achieving widespread vaccination. 1,2 However, all states also allow medical exemptions for those children unable to receive vaccines for medically contraindicated reasons. 3 Exemption laws in all but 2 states (Mississippi and West Virginia) also provide for nonmedical exemptions (NMEs) on the basis of parents’ religious, philosophical, or personal beliefs. NMEs are considered an important mechanism to balance child welfare and the protection of public health with parental rights. 4,5 Although some have argued that NMEs should not be allowed because parents who choose not to immunize their children put their own children and others at risk, 6 others believe that the negative consequences of exemption are not sufficient to justify violating parental autonomy. As concerns about vaccine safety have increased over the past 15 years, more parents are choosing to refuse or delay vaccines. 3,7 This increase in vaccine hesitancy can be seen at the point of school entry in the rising rates of NMEs. Furthermore, NMEs from school-entry immunization mandates are receiving increased policy and public health scrutiny because exemption rates within and across schools have significant epidemiological implications. Where NME rates are high enough to compromise herd immunity at the local level, the risk of vaccine-preventable disease outbreak increases. Understanding the spatial and social patterning of NMEs is therefore critical to infectious disease prevention and control efforts. Over the past decade, rising attention to vaccine hesitancy and NMEs has prompted several state legislatures to introduce, consider, and in some cases enact new exemption laws. In 2003, Arkansas, which previously only allowed medical and religious exemptions, started allowing philosophical exemptions on the condition that parents provided a notarized statement requesting an exemption, completed a vaccination education component, and signed a statement acknowledging the receipt of vaccination information. 8,9 Similarly, in 2003, Texas also started to allow philosophical exemptions, requiring those who wanted to exempt to obtain a form from the Texas Department of Health and declare their objections in an affidavit. 10 Conversely, Washington, Oregon, and California, all of which previously had lenient exemption policies and, particularly in the case of Washington and Oregon, very high exemption rates, recently made the process for claiming an exemption harder by requiring a signed statement from a health care practitioner that the parent had been informed of the risks and benefits of immunization. In the 2011–2012 legislative cycle, bills to tighten or eliminate NMEs were introduced in 3 states, whereas bills to expand or allow NMEs were proposed in another 10. 11 Continued increases in vaccine refusal and NME rates and the growing attention to NMEs in state legislatures underscore the importance of understanding the determinants of NMEs, the impact of state NME policies, and the epidemiological implications of NMEs for vaccine coverage, herd immunity, and disease outbreak risk. The goal of this systematic review, therefore, is to summarize the recent evidence on NMEs, including the prevalence of, trends in, and correlates of NMEs and the association of these exemptions and exemption policies with the incidence of vaccine-preventable disease.
