Measuring Multiple Dimensions and Indices of Nonvaccination Clustering in Michigan, 2008-2018.

Michigan experienced a significant measles outbreak in 2019 amidst rising rates of nonmedical vaccine exemptions (NMEs) and low vaccination coverage compared with the rest of the United States. There is a critical need to better understand the landscape of nonvaccination in Michigan to assess the risk of vaccine-preventable disease outbreaks in the state, yet there is no agreed-upon best practice for characterizing spatial clustering of nonvaccination, and numerous clustering metrics are available in the statistical, geographical, and epidemiologic literature. We used school-level data to characterize the spatiotemporal landscape of vaccine exemptions in Michigan for the period 2008-2018 using Moran's I, the isolation index, the modified aggregation index, and the Theil index at 4 spatial scales. We also used nonvaccination thresholds of 5%, 10%, and 20% to assess the bias incurred when aggregating vaccination data. We found that aggregating school-level data to levels commonly used for public reporting can lead to large biases in identifying the number and location of at-risk students and that different clustering metrics yielded variable interpretations of the nonvaccination landscape in Michigan. This study shows the importance of choosing clustering metrics with their mechanistic interpretations in mind, be it large- or fine-scale heterogeneity or between- and within-group contributions to spatial variation.

The Impact of Michigan's Nonmedical Vaccine Exemption Rule Change on Philosophical Exemption Rates.

To examine school factors associated with philosophical exemption rates among kindergarteners in Michigan from 2014, before Michigan's implementation of administrative rule 325.176 (12), to 2015, after the rule change revising the process for receiving nonmedical exemptions from school entry vaccines. The study explored the extent to which the factors-school type, geographical location, and socioeconomics-were associated with philosophical exemptions among kindergarteners before and after the rule change, using negative binomial regression and Spearman's Rho correlation. Philosophical exemptions decreased from 2014 to 2015 for all school types but remained highest among rural private schools. Urban private schools had the second highest exemptions with rates 2.22 times higher than those of urban public schools. Exemption rates among rural charter schools were double those of urban public schools, while rural public schools' rates were 1.22 times higher than those of urban public schools. Free and reduced school lunch eligibility had a strong inverse association with philosophical exemptions for both 2014 and 2015, with higher philosophical exemptions being associated with higher socioeconomic schools. Philosophical exemption rates decreased in the wake of the rule change; however, high philosophical exemptions, post rule change, were still associated with private schools, rural locations, and high socioeconomic status schools.

Geospatial analysis of nonmedical vaccine exemptions and pertussis outbreaks in the United States.

Because of increased numbers of recorded pertussis cases in the United States, this study sought to understand the role of nonmedical vaccine exemptions and waning immunity may have had on the resurgence of pertussis in the United States at the community level. We used geospatial scan statistics, SaTScan, version 9.4, to analyze nonmedical vaccine exemptions of children entering kindergarten in 2011 and 2012 and reported pertussis cases in 2012 for children in age groups 5 years and younger and 10 to 14 years. Eight statistically significant clusters of nonmedical vaccine exemptions in kindergarteners and 11 statistically significant clusters of pertussis cases in children and adolescents were identified and geospatially linked. Forty-five percent of the counties in the study had high rates of nonmedical vaccine exemptions. The proportion of kindergarteners with nonmedical vaccine exemptions was 2.8 times larger in the identified exemption clusters. In addition, 31 counties had geographic clusters of high rates of pertussis in children ages 10 to 14 years old, consistent with waning immunity. Our findings are consistent with the view that geographic clusters of nonmedical vaccine exemptions and waning immunity may have been factors contributing to community-level pertussis outbreaks.

Exploring the impact of the New York State repeal of nonmedical vaccination exemptions on student enrollment, absenteeism, and school workload: Perspectives from a survey of school administrators.

In June 2019, New York State (NYS) adopted Senate Bill 2994A eliminating nonmedical vaccine exemptions from school entry laws. Since student noncompliance with the law required school exclusion, we sought to evaluate the law's effects on student enrollment and absenteeism, and school workloads related to its implementation. In November 2019, we sent an electronic survey to NYS (excluding New York City) schools. Due to the COVID-19 pandemic, outreach was curtailed in March 2020 with 525 (14%) of 3,759 eligible schools responding. To account for non-response, results were analyzed using inverse probability weighting. After weighting, 39% (95% CI: 34%, 44%) of schools reported enrollment changes and 31% (95% CI: 26%, 36%) of schools reported absenteeism related to the law. In addition, 95% (95% CI: 93%, 98%) of schools reported holding meetings and/or preparing correspondence about the law, spending a mean of 14 (95% CI: 11, 18) hours on these communication efforts. Schools in the highest pre-mandate nonmedical exemption tertile (vs. lowest) were more likely to report enrollment and absenteeism changes, and higher workloads. While our results should be interpreted with caution, changes in student enrollment, absenteeism, and school workloads may represent important considerations for policymakers planning similar legislation.

Preventable Disease, the Case of Colorado: School District Demographics and Childhood Immunizations.

The objective of this study was to evaluate the impact of selected sociodemographic factors on childhood vaccination hesitancy and to define their role according to specific exemptions. This population-based cohort study utilized vaccination rate and sociodemographic data from 1st to 12th grade from 2017 to 2021 for all school districts in Colorado. Data included immunization status and exemptions for each vaccine, race, ethnicity, and free and reduced meal status. Data were evaluated through dimensional analysis and Generalized Linear Mixed Models. School districts with a higher representation of White students had lower immunization rates and use more personal exemptions while school districts with larger Hispanic populations and higher proportions of free and reduced lunches had higher vaccination rates and used more religious exemptions. Black and Pacific Islander populations had higher rates of incomplete vaccination records while Asian American population displayed increased vaccination compliance. Colorado is a robust example of how socioeconomic and cultural differences are important factors with a direct influence on vaccination rates. Future childhood vaccination campaigns and legislation should consider complex socioeconomic and cultural factors.

Measles outbreaks and public attitudes towards vaccine exemptions: some cautions and strategies for addressing vaccine hesitancy.

Today, the United States and countries throughout the world are experiencing measles outbreaks that have sickened thousands of children. From the Disneyland outbreak in 2014 to today, some states have responded with changes in laws on vaccine requirements and exemptions. In this article, we examine the history of vaccine laws, and using our 2015 survey data, explore to what extent the news coverage of the Disneyland outbreak altered parents' attitudes toward required vaccination and non-medical exemptions. We explore those results in the context of today's increasing polarized and politicalized battle over vaccine laws, and consider how health care providers and policy makers can work to improve public attitudes about vaccines.

Communicating About Immunizations.

A significant minority of patients and parents are vaccine hesitant, defined as having the desire to delay or defer immunizations despite easy access to vaccines. Vaccine hesitancy exists along a spectrum, from patients who are concerned but willing to accept the recommended vaccine schedule to those who wish to use a delayed schedule to those who refuse vaccines altogether. A strong recommendation in favor of a vaccine is the most important reason a patient or parent accepts the immunization. Structural changes, such as removing personal and religious exemptions for vaccines required for attending school, are effective tools in increasing vaccination rates.

Geographic hot spot analysis of vaccine exemption clustering patterns in Michigan from 2008 to 2017.

OBJECTIVE: This study explored vaccine exemption clustering in Michigan and examined whether vaccine exemptions clustered by exemption type (medical, religious, and philosophical). Furthermore, the study investigated whether Michigan's nonmedical vaccine exemption policy change had an impact on type-specific vaccine exemption clusters following its implementation. METHODS: The study used the ArcGIS optimized hot spot analysis tool to visually examine vaccine exemption clustering by type in Michigan. The study analyzed secondary kindergarten vaccine exemption data from 2301 elementary school buildings in Michigan for years spanning 2008 to 2015 and 2016 to 2017 post policy change. RESULTS: Clustering of vaccine exemptions by type was present both before and after implementation of the policy with fewer statistically significant features and differences regarding the distribution of hot spot clusters following the policy change. CONCLUSION: Considering the heterogeneity in vaccine exemption hot spot clustering by type can help to inform public health officials to areas/communities at high risk for vaccine preventable disease outbreaks. Such analysis can allow for the implementation of vaccine exemption interventions that are exemption type specific and tailored for a given area, thus maximizing impact and making best use of limited public health resources. This analysis was also able to showcase the impact of Michigan's nonmedical vaccine exemption policy on vaccine exemption hot spot clusters.

Impact of Nonmedical Vaccine Exemption Policies on the Health and Economic Burden of Measles.

OBJECTIVE: Despite relatively high national vaccination coverage for measles, geographic vaccination variation exists resulting in clusters of susceptibility. A portion of this geographic variation can be explained by differences in state policies related to nonmedical vaccine exemptions. The objective of this analysis was to determine the magnitude, likelihood, and cost of a measles outbreak under different nonmedical vaccine exemption policies. METHODS: An agent-based transmission model simulated the likelihood and magnitude of a measles outbreak under different nonmedical vaccine exemption policies, previously categorized as easy, medium, or difficult. The model accounted for measles herd immunity, infectiousness of the pathogen, vaccine efficacy, duration of incubation and communicable periods, acquired natural immunity, and the rate of recovery. Public health contact tracing was also modeled. Model outcomes, including the number of secondary cases, hospitalizations, and deaths, were monetized to determine the economic burden of the simulated outbreaks. RESULTS: A state with easy nonmedical vaccine exemption policies is 140% and 190% more likely to experience a measles outbreak compared with states with medium or difficult policies, respectively. The magnitude of these outbreaks can be reduced by half by strengthening exemption policies. These declines are associated with significant cost reductions to public health, the health care system, and the individual. CONCLUSIONS: Strengthening nonmedical vaccine exemption policies is 1 mechanism to increase vaccination coverage to reduce the health and economic effect of a measles outbreak. States exploring options for decreasing their vulnerability to outbreaks of vaccine-preventable diseases should consider more stringent requirements for nonmedical vaccine exemptions.

Nonmedical vaccine exemptions and pertussis in California, 2010.

BACKGROUND: In 2010, 9120 cases of pertussis were reported in California, more than any year since 1947. Although this resurgence has been widely attributed to waning immunity of the acellular vaccine, the role of vaccine refusal has not been explored in the published literature. Many factors likely contributed to the outbreak, including the cyclical nature of pertussis, improved diagnosis, and waning immunity; however, it is important to understand if clustering of unvaccinated individuals also played a role. METHODS: We analyzed nonmedical exemptions (NMEs) for children entering kindergarten from 2005 through 2010 and pertussis cases with onset in 2010 in California to determine if NMEs increased in that period, if children obtaining NMEs clustered spatially, if pertussis cases clustered spatially and temporally, and if there was statistically significant overlap between clusters of NMEs and cases. RESULTS: Kulldorff's scan statistics identified 39 statistically significant clusters of high NME rates and 2 statistically significant clusters of pertussis cases in this time period. Census tracts within an exemptions cluster were 2.5 times more likely to be in a pertussis cluster (odds ratio = 2.47, 95% confidence interval: 2.22-2.75). More cases occurred within as compared with outside exemptions clusters (incident rate ratios = 1.20, 95% confidence interval: 1.10-1.30). The association remained significant after adjustment for demographic factors. NMEs clustered spatially and were associated with clusters of pertussis cases. CONCLUSIONS: Our data suggest clustering of NMEs may have been 1 of several factors in the 2010 California pertussis resurgence.