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 initial search yielded 165 articles, with 64 full-text articles assessed for eligibility (see Figure 1 for Preferred Reporting Items for Systematic Reviews and Meta-Analyses flowchart). Of the full-text articles assessed, 5 were not related to exemptions, 9 were presentations, and 6 were commentaries, historical reviews, or otherwise not empirical studies, for a total of 20 excluded. We therefore included 44 studies in the review: 29 quantitative, 13 mixed, and 2 qualitative. Of the quantitative and mixed studies, most (27) were cross-sectional observational studies, 12 were time-series cohort studies, 1 was a retrospective cohort study, and 2 were case-control studies. Key elements of the 44 included studies are shown in Table 1.

Figure 1.

Flow diagram of study selection for systematic review of research on nonmedical exemptions from school immunization requirements.

Nonmedical Exemptions Prevalence and Trends

Nineteen studies summarized NME prevalence. Data from the Centers for Disease Control and Prevention's annual school immunization assessment showed a general increase in state-level NME rates over time, from 1.6% in 2009–2010[26] to 2.0% in 2011–2012[27] to 1.9% in 2012–2013,[28] an overall 19% increase (data for 2009–2010 and 2012–2013 are shown in Table 2). For 2012–2013, state exemption rates ranged from a low of 0.0% in Delaware to a high of 6.4% in Oregon (note that Mississippi and West Virginia do not permit NMEs). Thirteen state and metropolitan grantees had NME rates exceeding 3%, and 16 grantees had exemption rates below 1%. Since 2009–2010, 32 states have shown an increase in state-level exemption rates, 4 states and the District of Columbia have remained the same, 9 states have decreased their exemption rates, and 5 states did not have data for a longitudinal comparison. Since 2005–2006 (not shown in Table 2),[58] many states have seen a rough doubling of exemption rates, regardless of the initial rates. For example, between 2005–2006 and 2012–2013, Arkansas's exemption rate increased from 0.3% to 0.7%, California's rate from 1.3% to 2.8%, and Oregon's rate from 3.4% to 6.4%.

Although exemption rates varied considerably across states, several studies found even greater within-state variation, identifying both spatial and social clustering of exemptions.[8,33,37,55] For example, county-level NME rates in California ranged from 0% to 17% in 2010.[19] In Arizona, school-level exemption rates ranged from 0% to 68% in the 2010–2011 school year; 21% of schools had exemption rates higher than 5%, 8% had rates higher than 10%, and 3% had rates higher than 20%.[17] The phenomenon of clustered exemptions is important both to understand the determinants of spatial and social patterning of vaccine hesitancy and refusal and to identify the epidemiological implications of increased disease outbreak risk associated with the clustering of unvaccinated children. In addition, 1 study in Arkansas showed that although exemption rates, both nonmedical and medical, were increasing in general, the proportion of philosophical exemptions was increasing relative to other exemptions.[8] That same study also showed that exemption rates were increasing faster among kindergarten children than among any other age group requiring vaccination documentation.[8]

Sociodemographic, Attitudinal, and Behavioral Correlates

Eighteen studies reviewed included results related to correlates of NMEs. Two studies that surveyed parents who exempted, delayed, or refused vaccines found that they tended to be White and college educated and to have relatively high incomes compared with parents who did not seek exemptions or who did not delay or refuse vaccines.[18,19] Similarly, another study found that high exemption clusters were associated with higher socioeconomic status characteristics.[50] However, 2 studies showed a slightly contradictory trend. In 1 survey of Oregon parents, those who exempted were more likely to have a lower socioeconomic status than nonexemptors.[58] In another study, parents with lower household incomes were more likely to oppose compulsory vaccination than those with higher incomes.[17] Parents who exempted from school vaccine mandates were also more likely to have a lifestyle categorized as "alternative living," which includes veganism or vegetarianism, organic gardening, and use of natural healing remedies.[34,50]

The sociodemographic composition of the school and surrounding community also predicted exemption rates. Higher exemption rates were associated with higher proportion of Whites, higher percentage of college graduates, higher median household income, and lower percentage of families in poverty at the census tract, zip code, or school district level.[16,17,47] Studies found more exemptions in rural than in urban school districts,[46,47] and exemption rates were higher, and increased faster, among private than public schools.[47]

Perceptions of information provision and sufficiency were correlated with exemption preferences. Parents who did not believe they had enough immunization information were more likely to believe that states should grant exemptions on the basis of religious and personal beliefs and that parents should be allowed to obtain exemptions for their child even if it raised the risk of disease for everyone else.[35] However, a majority of parents in an Indiana measles outbreak who exempted their children believed they had access to enough information on vaccination.[33] Trust was also a consistent correlate of seeking exemptions: parents who filed exemptions were more likely to be skeptical of the government, pharmaceutical industry, and medical community and to distrust information, or not rely on material, coming from those sources.[7,33,34,50,55] The evidence was inconsistent on the sources of information most commonly consulted by parents who exempt. Although some read peer-reviewed medical journals,[34] others cited media reports questioning vaccine safety.[39] Internet research was frequently reported by providers as a source of parental information; however, 1 study showed that a majority of exemptors did not use the Internet when researching vaccines even though they had Internet access.[41]

Not surprisingly, negative attitudes and beliefs about vaccines predict exemption. Exemptors and parents who have considered exempting are significantly more likely than nonexemptors to have strong vaccine concerns and negative attitudes about immunizations and immunization safety.[33,36,39,41,50] A common and persistent concern is the belief that vaccines harm the health of the child and cause adverse reactions or developmental problems such as autism.[38–41,53,55,57] Other concerns identified in the literature included fear of acquiring the disease from the vaccine, dangerous chemicals or preservatives in vaccines, the child's receiving too many shots at 1 time, and overloading the immune system.[36,39–41,57] Another common belief associated with exemption is that vaccination is unnecessary because of low perceived susceptibility to and severity of vaccine-preventable diseases.[17,34,50]

There also appears to be a strong association between parental and provider immunization beliefs. In 1 study that surveyed parents of exempted or nonexempted children, parents had a 12 times greater odds of believing healthy children do not need immunizations if their provider also held this belief than parents whose provider did not hold this belief.[42] Parental beliefs in vaccine safety and in vaccine mandates impeding parental choice were also correlated with provider beliefs.[42] This study was not able to determine whether parental views are shaped by interactions with health care providers or whether parents choose health care providers with similar vaccine beliefs; both dynamics are likely operating.

Exemptions are sometimes sought for some vaccinations but not others. In the 2009–2010 school year in Arkansas, although most (71%) exemptions were requested for all vaccines, 9% were requested for 2 or more vaccines and 20% for a single vaccine.[8] Another multistate study showed that 75% of children with NMEs had received at least some vaccines (based on parent report), and 22% of the parents who filed exemptions responded that their children were fully vaccinated.[50] The measles–mumps–rubella, varicella, and hepatitis B vaccines were also reported as the most frequently exempted vaccines.[8,53]

Although many parents seek exemptions for philosophical reasons, some parents also exempt out of convenience or because of poor access to immunization services. Parents who cannot locate child immunization records may find that filing a NME is more convenient than tracking down lost records.[40,52] School personnel may therefore also affect exemption rates. Children attending schools at which nurses (vs other professional staff) are responsible for tracking immunizations were less likely to have an exemption.[51] School-based immunization clinics increased the number of fully immunized students (and decreased exemptions), which supports the idea that at least some exemptions are obtained for reasons of convenience rather than conviction.[46]

State Exemption Policies

Fourteen studies focused on state exemption policies. States have the authority to mandate specific immunizations for day care and school attendees. All states allowed exemptions to immunization mandates for medical contraindications; 30 states and the District of Columbia allowed religious exemptions but no philosophical exemptions; 18 states allowed both religious and philosophical exemptions; and 2 (Mississippi and West Virginia) did not allow either.[59] Studies have consistently found that allowing philosophical and religious exemptions increases exemption rates and decreases vaccination rates.[8,11,31,43,44,56] For example, after Arkansas introduced philosophical exemptions in 2003, the total number of exemptions granted increased from 651 in 2002–2003 to 764 in 2003–2004 and 1145 in 2004–2005.[8,56] Furthermore, in states with philosophical exemptions, such exemptions have increasingly encompassed an overwhelming majority of all exemptions.[8,31,56] Allowing philosophical exemptions affected not only exemptions for school-aged children but also the rates of unvaccinated children too young for school-entry mandates.[54] Residence in a state that offers philosophical exemptions was also associated with parents' opposition to compulsory vaccination for school entry, although the direction of causality was not clear.[38]

State exemption rates also appeared to be correlated with the ease with which NMEs can be obtained. Studies have consistently found that states with easier exemption requirements (in terms of paperwork or the effort required) have higher exemption rates and vice versa.[11,29,44,45,48,52] Again, causal inference is challenging here: Although stricter exemption policies may lead to lower exemption rates, legislators with constituents who have vocal vaccine-refusing parents may also be more likely to enact lenient exemption policies.[11] For example, the 2003 Arkansas law that allowed philosophical exemptions but that required an educational module and an annual application process neither increased nor retarded the increase in exemptions compared with other states in the region that did not require such rigorous requirements.[8] In terms of long-term trends, exemption rates in states with easy exemption regimes increased significantly over time, whereas states with medium to difficult exemption regimes showed no significant increase, although rates have been increasing in recent years across all states, regardless of exemption regime.[44,45] Even in states that do not grant philosophical exemptions, such as New York, religious exemption rates are increasing and are now comparable to rates in those states that permit philosophical exemptions,[37] with easier religious exemption procedures associated with higher exemption rates.[11] This likely indicates that parents seek religious exemptions for philosophical or personal beliefs, and religious exemption processes should be scrutinized as well.[11,37]

Crucially, easier exemption regimes were associated not only with higher exemption rates but also with higher disease outbreak risk. For example, pertussis incidence from 1986 to 2004 was 41% higher in the 6 states that accepted parental signature as sufficient proof of immunization than in the 45 states and the District of Columbia that required medical records, suggesting that exemption policies affect vaccination rates and therefore disease incidence.[44] Despite this strong association, even in states in which exemptions were easiest to obtain, mean vaccination coverage rate remained higher than 90%. Easy exemption regimes clearly do not produce universally high exemption rates across an entire state. The spatial and social patterning of parental preferences can interact with the variations in school-level administration and implementation of immunization and exemption laws to produce substantial heterogeneity in exemption rates both within and across counties independent of exemption regimes.[29,43,47,52]

Epidemiological Implications of Nonmedical Exemptions

Seventeen studies assessed the epidemiological implications of NMEs. Exemptions from mandated immunizations increased individual risk for contracting a disease and population risk for disease outbreak. Exemptors were more likely to acquire measles and pertussis than vaccinated children,[21,37] with a 22- to 35-times higher risk for measles[49] and a 6-times higher risk for pertussis.[31] In outbreaks of vaccine-preventable childhood diseases in the United States, many affected children had exemptions or were otherwise unvaccinated because of parental philosophical or religious beliefs.[20,21,23–25,55] The evidence was most striking in the case of measles.[23,29,32] For example, in 1997 when a total of 138 cases were reported in the entire United States, 1 county in Utah had an exemption rate nearly 6 times the national average and experienced a measles outbreak with 107 cases. Half of these cases were people who had been vaccinated, showing that high exemption rates can put nonexemptors at risk, too.[23] Of 131 confirmed measles cases in the United States in 2008, 112 were not vaccinated and of those, 63 (66%) had not been vaccinated because of religious or philosophical beliefs.[25] In 2 measles outbreaks in Washington State and Illinois in 2008, 100% of 16 children and 25 of 29 children, respectively, had not received the measles vaccine because of their parents' beliefs.[25] In 2 measles outbreaks in Utah in 2011, 9 of 13 people who contracted measles were unvaccinated because of personal belief exemptions.[22] The evidence is not limited to measles: from 1992 to 2000, of the 15 cases of tetanus in children, 12 were not vaccinated for nonmedical reasons.[30]Furthermore, of the school-based outbreaks in Colorado examined from 1987 to 1998, schools with pertussis outbreaks had more exemptors (mean = 4.3%) than schools without pertussis outbreaks (mean = 1.5%, P = .001).[31]

At the community level, studies have found that geographic clusters of vaccine exemptors are associated with outbreak risk and with higher incidence of vaccine-preventable disease.[21] In California, census tracts within a cluster of NMEs were more likely to also be in a pertussis cluster than those outside a cluster of NMEs; the incidence of pertussis was also higher in NME clusters than outside of those clusters.[16] Local-area exemption rates have been shown to be positively associated with the incidence of measles and pertussis even in vaccinated children, and epidemiological models based on outbreak data have shown that an increase in exemptions will lead to higher incidence of measles in nonexempt populations.[18,31,37,43,49] Decreased vaccination coverage as a result of exemptions could also lead to a significant increase in the severity and duration of an outbreak, depending on the population size.[18]