Researchers used spatial analysis software and electronic medical records to identify clusters of underimmunization and vaccine refusal among Kaiser Permanente members in Northern California, according to a study published today in the journal Pediatrics.

Public domain image/National Atlas of the United States
Public domain image/National Atlas of the United States

Children are considered to be underimmunized when they miss one or more recommended vaccine doses before age three, while vaccine refusal means not allowing a child to receive any vaccines.

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 and 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. To identify the clusters of underimmunization and vaccine refusal, researchers used sophisticated spatial analysis software, which allowed them to examine health factors in relation to geography.

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 is associated with elevated risk of vaccine-preventable disease, while nonmedical immunization exemption and refusal have been associated with increased community risk of measles and pertussis.

“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.”

Dr. 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.

Read the rest of theĀ Kaiser Permanente news release HERE