(Reuters) - Families with underimmunized or unvaccinated children tend to cluster together, a new study shows.

Underimmunization is tied to an increased risk of vaccine-preventable diseases, the researchers write in the journal Pediatrics.

“We now have the opportunity to use really sophisticated methods to identify these kinds of clusters of undervaccination or vaccine refusal,” said Dr. Tracy Lieu, the study’s lead author from the Kaiser Permanente Division of Research in Oakland, California.

“With tools like these we have much more power and ability to identify emerging issues than anyone would have 20 or 30 years ago,” she said.

While the Centers for Disease Control and Prevention reports that vaccine rates remain high, some vaccine-preventable diseases, like measles, have made comebacks in recent years.

Lieu and colleagues hope that by identifying clusters of people who refuse to vaccinate their children or refuse certain shots, researchers can target prevention efforts. For the new study, they analyzed records for 154,424 children born between 2000 and 2011 in 13 California counties.

All were members of Kaiser Permanente Northern California, a large nonprofit health plan. Using those records, they were able to identify five clusters with higher rates of three-year-olds who had missed at least one vaccine.

About 18 percent to 23 percent of children in those clusters were underimmunized, compared to about 11 percent of children outside those clusters.

Children whose parents refused vaccines were also clustered in geographic areas. Rates of refusal ranged from about 6 percent to about 14 percent in the clusters, compared to about 3 percent outside of those areas. In addition to targeting those areas for public health messages, Lieu said doctors can be more alert to the possibility of vaccine-preventable disease.

“If you know there is a cluster of undervaccination or vaccine refusal in a certain area, you may be more vigilant,” she said.

The study can’t say why these areas of underimmunization and vaccine refusal formed, however.

“This really identifies a nice mechanism to identify where there might be a problem with misconceptions or whatever the reason is, but an area where resources can be well spent to provide more focused information and dispel and misinformation people may have,” said Dr. Amar Safdar, an infectious disease expert at NYU Langone Medical Center who was not involved with the new study.

Safdar said parents sometimes believe vaccines are dangerous.

“The reason why science and medicine is behind vaccination is that there is no identifiable damage to the kids,” he said.

SOURCE: http://bit.ly/1BtniTp Pediatrics, online January 19, 2014.