Sign In

Press Release

January 18, 2015

Researchers have used spatial analysis software and electronic medical records to identify clusters of underimmunization and vaccine refusal in Kaiser Permanente’s Northern California region, according to a study published Jan. 19 in the journal Pediatrics.

“This research confirms anecdotal reports of underimmunization clusters,” said Tracy A. Lieu, MD, MPH, the study’s lead author, a Kaiser Permanente pediatrician, and director of the Kaiser Permanente Division of Research. “In addition, we found clusters in places we hadn’t anticipated.”

The Centers for Disease Control’s immunization schedule recommends a minimum of 17 separate injections during a child’s first two years of life, including for hepatitis A and B, diphtheria, tetanus, pertussis, influenza, polio, measles, mumps, rubella, and pneumococcal virus.

Underimmunization — missing one or more recommended vaccine doses before age three — ranged from 18 percent to 23 percent within clusters, compared with 11 percent outside clusters. Between 2010 and 2012, geographic clusters of underimmunization were found in the East Bay (Richmond to San Leandro); Sonoma and Napa counties; a small area of east Sacramento; northern San Francisco and southern Marin counties; and a small area of Vallejo. “Shot limiting,” in which parents limit the number of injections or antigens that children receive during a pediatric visit to two or fewer, was found to cluster in similar areas. 

Vaccine refusal — not allowing a child to receive any vaccines — ranged from 5.5 percent to 13.5 percent within clusters, compared with 2.6 percent outside clusters. Between 2010 and 2012, geographic clusters of vaccine refusal were found in the East Bay (El Cerrito to Alameda); Marin and southwest Sonoma counties; northeastern San Francisco; northeastern Sacramento County and Roseville; and a small area south of Sacramento.

The study reviewed the immunization records of more than 154,000 Kaiser Permanente Northern California members between birth and 3 years old. All the children were born between 2000 to 2011 and were covered continuously by Kaiser Permanente, which provides health care for about 40 percent of the insured population in 13 Northern California counties.

“Kaiser Permanente has among the richest electronic medical records in the world,” Lieu said. “This is the first time that spatial analysis techniques have been applied to real-time vaccine data.”

Lieu noted that this study will be useful for targeting outreach efforts in particular areas, although it was not designed to figure out why children in some areas are less likely to be fully immunized.

“Everyone in the Kaiser Permanente health care system has access to vaccines, and since childhood vaccination is covered by insurance, financial barriers are not an issue,” Lieu said. “Our findings raise awareness that there may be communities where parents have more vaccine hesitancy and may be interested in more information or more in-depth conversations with their children’s doctors.”

This research is part of a larger study on parent preferences and vaccination funded by the Patient-Centered Outcomes Research Institute.

In addition to Lieu, co-authors of the study are G. Thomas Ray, MBA, Kaiser Permanente Division of Research; Nicola P. Klein, MD, PhD, Kaiser Permanente Vaccine Study Center; Cindy Chung, MD, Kaiser Permanente San Rafael Medical Center; and Martin Kulldorff, PhD, Harvard Pilgrim Health Care and Harvard Medical School.