Nonmedical Exemptions From School Immunization Requirements: A Systematic Review

Eileen Wang; Jessica Clymer, BA, BSN; Cecilia Davis-Hayes, BA; Alison Buttenheim, PhD, MBA


Am J Public Health. 2014;104(11):e62-e84. 

In This Article


Our review of the evidence on NMEs from mandated school-entry vaccines shows increasing NME rates in the United States, with substantial variation in rates across schools, regions, and states. Parents seeking exemptions are more likely to be White and of higher socioeconomic status and to be skeptical of the government and of the pharmaceutical medical industry. Parents who exempt are more likely to have concerns about vaccine safety and adverse effects, particularly if their health care provider shared these concerns. Exemption rates are also associated with state laws and school administrative policies: states in which it is easier to file an exemption have higher exemption rates than states in which it is harder to do so, and this, in turn, is associated with higher disease risk. Epidemiologically, higher exemption rates are associated with lower vaccination rates and therefore higher individual risk of contracting disease and higher community outbreak risk.

Although overall vaccine coverage generally remains high in the United States, our review shows both higher prevalence and more intensive geographic clustering of NMEs over time. Clustering is particularly associated with disease outbreaks because herd immunity is compromised in areas with higher proportions of undervaccinated children.[60] Clustering of exemptions can result from both selection effects—like-minded people tend to live near and socialize with each other—and social influence or diffusion effects, through which parents learn about social norms and about variations in the implementation of state and school immunization requirements and in provider responses to requests for exemptions.[33] Further research should disentangle these effects to better inform interventions to preserve herd immunity at the local level.

The determinants and epidemiological implications of NMEs are varied and multifactorial, suggesting that multiple intervention strategies are needed. An important underlying factor is the true immunization status of exempted children. If exempted children are completely unvaccinated, the disease outbreak risk may be higher than that estimated using exemption rates. For example, a study that used child medical records showed a 23-fold higher risk of pertussis infection among children whose parents refused pertussis vaccination than among vaccinated children,[61] compared with the 6-fold higher risk found in a study that used exemptions to proxy this effect.[31] Although additional studies that directly used data of unvaccinated children rather than those of exempted children have shown that the individual risk for contracting disease is increased,[62,63] further research is needed to ascertain the validity of NMEs as a proxy for vaccination status in determining population-wide, epidemiological risk. This would have implications for administrative and implementation purposes—if high exemption rates are driven by parents not having complete vaccine records accessible, then reducing exemptions through better record keeping is not likely to reduce disease outbreak risk, because these children are probably fully or near-fully vaccinated.[40]

Previous studies have demonstrated that parental exemption decisions are shaped in part by state exemption policies. State-level policy changes that make exemption more difficult or burdensome for parents, such as have been implemented in Vermont, Washington State, and recently in California, can therefore both decrease exemption rates and increase vaccination coverage.[64] However, as states look to legislative action either to reduce exemptions or to accommodate parent preferences for greater freedom to exempt, the distinctions among religious, philosophical, and personal belief exemptions will warrant further attention. When philosophical exemptions in Arkansas were introduced, religious exemptions decreased, implying substitution of religious with philosophical exemptions.[8] States with a relatively easy religious exemption option but no philosophical exemption option have been shown to have higher overall rates of exemption than those with more burdensome religious exemptions and no philosophical exemptions, suggesting that vaccine-hesitant parents with philosophical but not religious objections to vaccination may be willing to use a religious exemption when the process is simple.[11] The experience of California, whose new exemption law makes attaining a personal beliefs exemption harder but adds a religious option for parents who claim that they cannot seek medical advice or attention, will be important to monitor in the coming years.[65,66]

Furthermore, regulations related to vaccine mandates and exemptions are implemented by school and district officials, and both school culture and administrative procedures will affect implementation. For example, California's new exemption law allows credentialed school nurses to sign the health provider attestation of vaccine counseling. Not all schools have school nurses on site, and school districts vary in their recommendations to school nurses about providing signatures for exemption requests. There is also considerable within- and across-state variation in, for example, the kindergarten registration process (when and where it occurs and what forms and documentation are required at the time of registration) and the publication of exemption data.[18] Evaluation of the impact of exemption legislation should acknowledge and exploit this variation. Finally, careful evaluations of the impact of new state policies on parent preferences, school-level procedures, and exemption rates will be needed to inform future legislative initiatives and to identify the extent to which convenience, rather than conviction, is driving current exemption rates. For parents whose decision to refuse vaccines is rooted in deep-seated beliefs, however, stricter state policies for obtaining exemptions are not likely to change attitudes or behaviors; as such, these parents may nevertheless decide to exempt their child despite any stipulations the government places on obtaining exemptions.[67] Because previous studies are inconsistent about the best way to address persistent vaccine hesitancy and refusal in the pre-school years, further innovation is needed in this area.[68]

As exemption rates climb, state health and education officials are eager to prevent further increases. Prevention strategies can be implemented at 2 time points. The first is during the prenatal period and throughout early infancy, when health care providers and public health messaging can encourage adherence to the recommended immunization schedule—a method that the United Kingdom uses without compulsory vaccination laws.[69] To do this counseling effectively, health care providers need clear, evidence-based, tailored counseling messages that can be delivered in the span of a brief well-child visit; although some resources exist, they are not widely used and tend to rely on conventional health education and promotion frameworks.[7] There is also variation in provider approaches to vaccine hesitancy, and certain providers may choose to dismiss parents who refuse vaccines, thereby driving them to a specific group of other providers. Conversely, parents may simply choose providers who have similar vaccine beliefs or who will accommodate requests for alternative schedules.[42] However, if vaccine-hesitant parents cluster in a smaller number of provider practices that will accommodate alternative schedules, the risk of exposure to vaccine-preventable diseases increases for this population.[70] Finally, financial incentives for both parents and providers have also been used in countries such as the United Kingdom and Australia.[69]

A second prevention strategy uses legislation and regulation to reduce requests for exemptions at the time of school entry by making the exemption process more difficult or burdensome—for example, by requiring parents to provide evidence of vaccine counseling from a health care provider.[11] Several states including Washington, California, and Vermont have recently implemented such legislation.[71–73] However, again, this strategy is more likely to be effective for parents with mild vaccine hesitancy or for those for whom exemption is a matter of convenience; for parents with strong antivaccine views, mandating risk–benefit counseling long after they have decided to delay or opt out of some vaccinations may actually backfire and cause protests or more mistrust if they feel the government has overstepped its boundaries in both mandating vaccinations and adding restrictions to the exemption process.[67,69]

We note some important limitations to this review. Many included studies were cross-sectional, and therefore we cannot ascertain the direction of causation nor completely rule out confounding. Several studies also relied on survey data, with the potential for selection or nonresponse bias. Population-level data from epidemiological studies may be susceptible to misclassification or measurement error, leading to information biases. Retrospective studies of parental beliefs are subject to recall bias. Many studies were specific to 1 or a few states, limiting generalizability. In addition to individual study limitations, the heterogeneity of study designs and outcomes precluded a quantitative meta-analysis from this systematic review, which would have been useful for analyzing quantitative trends. Many studies were also descriptive and were easily designated as high quality by the Quality Assessment Tool for Systematic Reviews of Observational Studies. As a result, quality assessment may not have been as rigorous for descriptive qualitative studies. We also excluded any studies without the mention of exemptions, even if they stated that the parents refused vaccinations for their child. This therefore could have left out other articles that are highly related to this topic but did not specifically discuss exemptions.

Vaccine mandates for school entry have been instrumental in sustaining herd immunity. Herd immunity against vaccine-preventable diseases is a valuable public good and a societal asset worth protecting. We found consistent evidence of rising rates of NMEs from school-entry vaccine mandates and of the association of exemption rates with outbreak risk. We have also found that stricter exemption laws can decrease or restrict the growth of these rates and thereby reduce outbreak risk. Interventions such as these, in addition to other strategies that address vaccine hesitancy and refusal before children reach school age, are therefore important to implement to maintain vaccination coverage across the United States and prevent outbreaks of disease.