Clustering of Vaccine Refusal = Pertussis Outbreak

October 16, 2013

Clustering of Vaccine Refusal = Pertussis Outbreak

  1. Robert S. Baltimore, MD

Geographic clustering of children who receive exemptions from vaccination can leave them at risk for pertussis.

  1. Robert S. Baltimore, MD

In 2010, 9120 pertussis cases with 10 deaths were reported in California — the highest numbers since 1947. Although waning immunity has been proposed as a major cause, clustering of unvaccinated children might also have played a role.

To examine this possibility, researchers analyzed spatial clustering of nonmedical exemptions (NMEs) for children entering kindergarten from 2005 through 2010 and space-time clustering of pertussis cases with onset in 2010 in California. They hypothesized that if children obtaining NMEs and pertussis cases clustered spatially, and if there was statistically significant overlap between clusters of children with NMEs and cases, then clustering of NMEs might partially explain pertussis outbreaks despite a reported high overall vaccination rate in the state.

During 2010, there were 39 statistically significant geographic clusters of high NME rates. Census tracts within an NME cluster were more likely than those outside an NME cluster to be in a pertussis case cluster (odds ratio, 2.47; 95% confidence interval, 2.22–2.75). This association remained significant after adjustment for sociodemographic variables. In the affected areas, clusters of both NMEs and pertussis cases were associated with factors characteristic of high socioeconomic status.


This study reinforces previous information I had read about clustering of vaccine refusers, and I have cautioned vaccine questioners/refusers who believe they are protected by herd immunity. The findings should be a warning to those who take advantage of certain states' lax approach to allowing immunization exemptions.

Editor Disclosures at Time of Publication

  • Disclosures for Robert S. Baltimore, MD at time of publication Editorial boards Current Opinion in Pediatrics; Infectious Diseases in Children


Reader Comments (2)

CHRISTI HILL Other Healthcare Professional, Pediatrics/Adolescent Medicine, public schools

DoloresGeddesBurke-- do you think that the parents would at least think again if they were to read the statistics cited in the article?

Dolores Geddes Burke B.S., M.A., Ed. D. Other Healthcare Professional, Other, retired prof emeritus, U of Southern California, Dept of Kinesiology and Exercise Physiology

There is a critical need to do more research on the topic of child vaccination safety but also to disseminate info GREATLY in related social media networks. The Florida outbreaks in Pertussis make this effort essential to me and my family in Florida. I am very alarmed that well-educated, intelligent grandchildren of mine will not vaccinate their children. What can be done to alert the public MORE than has been done to date?
I truly think that there is an insidious unrecognized ignorance in the general public that prioritizes gossip from alarmist celebs like Jenny McCarthy or even a small group of physicians... to NOT vaccinate. I do not want to wait for a decade or two to learn of the infectious diseases in children that were not prevented.

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