Examining the spatiotemporal evolution of vaccine refusal: nonmedical exemptions from vaccination in California, 2000–2013

Abstract

BackgroundVaccine hesitancy continues to be an issue throughout the United States, as numerous vaccine hesitant parents are choosing to exempt their children from school-entry vaccination requirements for nonmedical reasons, despite the safety and effectiveness of vaccines. We conduct an analysis of how vaccine refusal, measured by the use of nonmedical exemptions (based on personal or religious beliefs) from vaccination (NMEs), evolved across space and over time in California.MethodsUsing school-entry data from the California Department of Public Health, we examined NMEs for students entering kindergarten in California from 2000 to 2013. We conduct global and local spatial autocorrelation analysis to determine whether NME use became more geographically clustered over the study period and whether the location of local clusters of high use were temporally stable. We conducted a grouping analysis that identified the general temporal trends in NME use over the time period.ResultsThe use of NMEs increased from 0.73% of all kindergarteners in 2000 to 3.09% in 2013 and became more geographically clustered over the study period. Local geographic clusters of high use were relatively isolated early in the study period, but expanded in size over time. The grouping analysis showed that regions with high NME use early in the study period were generally few (15% of all US Census tracts) and relatively isolated. Regions that had low initial NME use and moderate to large increases over the study period were located in close proximity to the initial high use regions. The grouping analysis also showed that roughly half of all tracts had 0% or very low NME use throughout the study period.ConclusionsWe found an observable spatial structure to vaccine refusal and NME use over time, which appeared to be a self-reinforcing process, as well as a spatially diffusive process. Importantly, we found evidence that use of NMEs in the initially isolated regions appeared to stimulate vaccine refusal in geographically proximal regions. Thus, our results suggest that efforts aimed at decreasing future NME use may be most effective if they target regions where NME use is already high, as well as the nearby regions.Electronic supplementary materialThe online version of this article (10.1186/s12889-018-5368-y) contains supplementary material, which is available to authorized users.

Opting Out: Individualism and Vaccine Refusal in Pockets of Socioeconomic Homogeneity

“…Third, our goal has been to identify a setting where PBE hotspots are especially likely to occur, but our theory does not explain PBE concentrations outside of homogeneous pockets (see non-bold cells in Tables 5 and 6). Additional theoretical and empirical work—such as Delamater and colleagues’ (2018) study of spatial spillover effects—is needed to understand other high-PBE settings.…”

“…Second, the state keeps accessible government records, including data on the percentage of elementary school students who receive vaccine exemptions and the educational attainment of students’ parents (a key predictor in our analysis). Third, in the years leading up to the measles outbreak, California had one of the highest PBE rates of all 50 states, with documented spatial clustering of PBEs (Carrel and Bitterman 2015; Delamater et al 2018). Fourth, due to its size, its large and varied economy, and its demographic diversity, there is a significant amount of variation in terms of the composition of communities in which schools are located.…”

“…There, a measles outbreak began at the Disneyland theme park in Anaheim, spread to 147 individuals in seven states, and prompted the state to eliminate PBEs. 2 Several studies have found that vaccine exemptions were concentrated in particular California communities and schools (Brennan et al 2017; Carrel and Bitterman 2015; Lieu et al 2015), and this clustering intensified in the years before the Disneyland measles outbreak (Delamater et al 2018). Delamater and colleagues (2018) also find evidence of spatial diffusion, as areas with an increase in PBEs were near areas that initially had high PBEs.…”

“…From a public health perspective, the most concerning issue is that vaccine exemptions cluster in particular communities and schools (Brennan et al 2017; Carrel and Bitterman 2015; Delamater et al 2018; Lieu et al 2015; Omer et al 2008). Recent research indicates these clusters persist even when states minimize access to exemptions through stricter vaccination policies (Gromis and Liu 2020).…”

Italian Immunization Goals: A Political or Scientific Heated Debate?

“…It has been observed also in developed countries, such as the US, where a decrease in vaccination coverage was observed in children. This was mainly induced by a substantial increase in vaccine hesitancy among parents who chose to excuse their children from school-entry vaccination requirements for non-medical reasons (Delamater et al, 2018). A decrease in vaccination coverage was observed in US also for adult patients, as highlighted by a recent study that analyzed data from the 2015 National Health Interview Survey; it confirmed that, except for a moderate gain for some vaccines, coverage was low (Williams et al, 2017).…”