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.
Highlights
Vaccine 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
For nonmedical exemption (NME) use from 2000 to 2013, both I and G increased over time at each level of data aggregation, suggesting that both processes were occurring in California over this time period, e.g., proportional increases with a steady background rise in NME rates as well
We examined NMEs over a 14year time period in California that was devoid of changes to large-scale vaccine-related policy in an effort to focus on how the changes in vaccine-related behavior manifested in space over time
Summary
Vaccine 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. While vaccine hesitancy is not a new phenomenon [2] in the US, recent increases in the number of parents that refuse vaccination for their children [3], as well as recent outbreaks of VPDs such as pertussis and measles [4, 5], have resulted a renewed interest in understanding vaccine-related behavior This phenomenon is not constrained to the US; numerous countries around the world are contending with issues stemming from vaccine hesitancy, including reduced levels of coverage and corresponding VPD outbreaks [6, 7]. More than half of all states have considered and/or passed legislation that modified their existing NME requirements, including efforts to make NMEs both easier and more difficult to acquire [3, 9, 12]
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