According to a new study, identification of geographic clusters in which children have higher rates of under-immunization, or whose parents completely refuse vaccination, can help identify similar pockets of vaccine underutilization and help health care providers better concentrate on their approach to provide immunization interventions around the country.

The study has been published in the journal Pediatrics.

Dr. Tracy A. Lieu of Kaiser Permanente Northern California, Oakland, and her associates wrote that for optimal public health and patient care, clinicians and health care systems should preferably tailor care to their communities.

"The ability to identify clusters of underimmunization and vaccine refusal would help providers focus their efforts on the parents in communities with the greatest concerns, as well as identify areas at elevated risk for outbreaks of vaccine-preventable diseases", said Dr. Tracy.

Dr. Tracy A. Lieu also said that nonmedical exemptions from immunization in California clustered geographically and were related to clusters of pertussis cases. In a retrospective cohort study, Dr. Lieu and her co-investigators observed children, aged from birth to age 36 months, with continuous membership in the Kaiser Permanente Northern California between January 1, 2000, and December 31, 2009.

Overall 154,424 children in 13 northern California counties were included in the study. Children were categorized as underimmunized if they missed at least one vaccine by age 36 months, while vaccine refusal was classified using ICD-9-CM codes V6405, V6406, or V6407, according to the International Classification of Diseases, Ninth Revision, Clinical Modification for subjects who refused even one vaccination at any time prior to age 36 months.

Spatial scan analysis of all the accumulated data unveiled five statistically important geographic clusters in which underimmunization was more noticeable, almost all located in the greater Sacramento and San Francisco metropolitan areas.