The roles of neighborhood composition and autism prevalence on vaccination exemption pockets: A population-wide study
Introduction
Parental concerns over vaccine safety are suggested to have overtaken health care access as the primary obstacle to immunization in high-income countries [1]. In the United States, parents are required by law to provide documentation of immunization for enrollment to any school or childcare facility. However, increasing numbers of parents are seeking non-medical exemptions to vaccine requirements [2]. Non-medical exemptions differ from medical exemptions in that they are requested by parents on the basis of personal or religious beliefs rather than granted by medical professionals when vaccination may present adverse health risks. Parents who have sought non-medical exemptions are more likely to have expressed strong vaccine concerns or vaccine hesitancy [3].
Anti-vaccine beliefs have been shown to be difficult to change, and policy changes to tighten immunization requirements are often met with resistance [4], [5]. Vaccine refusals threaten herd immunity, which requires immunization levels of approximately 90% [6].1 Although population vaccination levels continue to meet this threshold,2 the spatial clustering of children with non-medical exemptions [8], [9], [10] can compromise herd immunity locally. Concentrations of exempted children in certain areas increase the risk of vaccine-preventable disease outbreaks [11], [12]. Additionally, private schools, particularly those that adopt alternative education methods, have been shown to have higher rates of PBEs than public schools [13], [14].
When other interventions are ineffective or infeasible, preventing clusters of children with non-medical exemptions can preserve herd immunity. This study seeks to identify mechanisms underlying non-medical vaccine exemption clusters. First, we explore how the discredited association between vaccines and autism might have affected the spatial patterns of exemptions. Despite the importance of the discredited link between the Measles, Mumps and Rubella (MMR) vaccine and autism in the current wave of the anti-vaccine movement, this is the first study to use address-level data of children with autism diagnoses to study the relationship between prevalence of autism and clusters of vaccine exemptions. Like vaccine exemptions, autism diagnoses cluster spatially [15], [16] and have a positive socioeconomic (SES) gradient [17], [18]. Although many studies demonstrated that vaccines do not cause autism (see [19]), a substantial number of parents are still concerned about the alleged link [20], [21].
Specifically, how worried parents are about autism and vaccines may depend on where they live: parents living in neighborhoods with higher rates of autism may be more concerned about vaccine safety than parents living in neighborhoods where autism is rare. Vicarious learning—learning derived indirectly from hearing or observing the experiences of family members, friends, neighbors or acquaintances – has been consistently shown to affect our perception of health risks [22], [23]. Our address-level data on autism allow us to evaluate whether the clusters of vaccine exemption and autism diagnoses overlap spatially.
Second, previous studies have shown that non-medical exemptions are more prevalent in predominately white, high SES neighborhoods [8], [9], [10], [24], [25], [26], [13], [27]. Various mechanisms could account for the positive SES gradient of these exemptions, such the perceived risks of contagious diseases [28]. Despite the many findings on SES and non-medical exemptions, the relationship between SES and vaccine-related beliefs is unclear [29]. Low SES and ethnic minority parents have more vaccine safety concerns than high SES parents, even though they still vaccinate their children [20], [30].
That said, a concentration of high SES individuals among the small number of parents who actually seek exemptions is sufficient to generate a positive SES gradient. This study seeks to move beyond identifying correlates of exemption clusters by asking: is the sorting of families by SES into certain neighborhoods sufficient to explain large pockets of exemptions that span multiple schools? Why do neighborhoods with residents of similar SES have drastically different exemption rates? Moreover, do some socio-demographic factors have a limited geographical span of influence while others are more important for broader clustering? Understanding the geographical span of the socio-demographic correlates of exemptions will shed light on the underlying mechanisms generating these clusters and has implications for how policy may better address preventing clusters of unvaccinated children.
Section snippets
Personal beliefs exemptions
This study uses the California Department of Public Health (CDPH) annual data on non-medical, Personal Belief Exemptions (PBEs) from school vaccination requirements from 1998 to 2014.3 Schools and licensed childcare centers are required to report exemptions to the CDPH.
Distributions of PBEs by school type
The average PBE rates in California private schools and non-charter public schools included in our model in 2014 were 5.2% and 2.1%, respectively.
Discussion
As of 2016, 47 U.S. states permitted religious and/or philosophical exemptions [41]. California began prohibiting PBEs in 2016. However, disallowing PBEs may drive some parents to seek medical exemptions [42]. Banning PBEs could also concentrate unvaccinated children in independent study schools.
Conflict of interest statement
We have no conflict of interest to declare.
Acknowledgement
This research is funded by the UCLA Hellman Fellowship (2014–2015). The authors benefited from facilities and resources provided by the California Center for Population Research at UCLA (CCPR), which receives core support (P2C-HD041022) from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD).
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