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

Significance Pertussis has been on the rise in the United States, and, in 2012, the United States had the highest number of reported pertussis (whooping cough) cases since 1955. This study provides evidence of spatial clustering of nonmedical vaccine exemptions in kindergarteners and spatial clustering of pertussis cases in children age groups 5 years and younger and 10 to 14 years at the community level. The results suggest that states should reconsider allowing nonmedical vaccine exemptions. The data also suggest a need for the creation of a longer-acting pertussis vaccine or improved regimen and a revised vaccination schedule for the current acellular pertussis vaccine. 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.