Researchers have identified several geographic hot spots in the Bay Area where parents are not vaccinating their children, triggering concern about potential outbreaks of dangerous and preventable infectious diseases.

This unique study — which uses statistical software to match electronic medical records to home addresses of Kaiser patients — reveals precisely where physicians can target their vaccination efforts and detect disease outbreaks quicker.

One cluster is in the East Bay communities of El Cerrito, Berkeley, Oakland and Alameda, where parents rejected vaccines for 10.2 percent of children. The second was in the northern part of San Francisco, as well as Marin County and the southwestern part of Sonoma County, with a 6.6 percent rate of vaccine refusal.

“Anecdotally, doctors have reported that a lot of parents in a particular neighborhood or county have hesitations about vaccines,” said lead investigator Dr. Tracy A. Lieu of Kaiser’s Division of Research, based in Oakland. “This is the first time we’ve used computers to actually find these clusters.”

Specifically identified were the San Francisco neighborhoods of the Marina, Pacific Heights and Richmond; in Marin, the cities of Mill Valley, Sausalito, Belvedere, San Rafael and rural West Marin towns such as Bolinas.

By comparison, there was a 2.6 percent rate of vaccine refusal among Kaiser Northern California members outside of these clusters.

The team also detected clusters of under-immunization — where between 18 and 23 percent of children received some, but not all, vaccines — in similar geographic areas, compared with 11 percent outside clusters.

Kaiser Permanente’s electronic medical record system, among the most extensive in the world, is a rich resource for research, said Lieu. The study analyzed the immunization records of more than 154,000 Kaiser Permanente Northern California members between birth and 3 years old. Kaiser provides health care for about 40 percent of the insured population in 13 Northern California counties.

They studied compliance with the Centers for Disease Control’s immunization schedule, which requires 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.

The Kaiser study did not find elevated rates of unvaccinated children in other regions of the Bay Area.

But a previous study of average vaccination rates in all Bay Area children, not just Kaiser members, found that the most vaccinations are in Contra Costa County and Santa Clara County, where 93.6 percent and 93.5 percent of children are vaccinated, respectively. The lowest were Santa Cruz County, with 82.15 percent, and Marin, with 82.02 percent.

One exception to Contra Costa County’s high vaccination rate is East Bay Waldorf School, a private school in El Sobrante, where county officials found a “personal belief exemption” rate of 50 percent.

Doctors say non-vaccination is dangerous because it threatens what’s known as “herd immunity.” If enough children are vaccinated, the whole population is protected. But if even a small number of children aren’t getting their shots, the immunity rate of the entire community can drop below safe levels.

The Kaiser study is significant because all children are insured and thus have equal access to preventive care. What it reveals, instead, are cultural differences.

Asian children are more likely to be vaccinated than white, Latino or African-American children, the study found.

In more affluent communities, “parents have more questions about vaccines,” and may reject them, Lieu said. In poorer communities, parents struggle to get time off work for doctors’ appointments.

Vaccine opponent Cynthia Cournoyer of Grants Pass, Oregon, said that parents are feeling overwhelmed by the number of vaccines. “They’re being inundated with so many — sometimes nine different vaccines in one visit,” she said.

Cournoyer, whose three children were not vaccinated, added that “parents hear and see what is happening to their children,” such as developmental delays, a contention disputed by physicians.

In California, a parent or guardian can refuse a vaccination if they file a letter with the school’s governing board that immunization “is contrary to his or her beliefs.” Parents can also file a statement from their physician stating that immunization wouldn’t be safe for the child.

But refusing a vaccine puts other people at risk, as well: infants who are too young to get shots, children who haven’t had their full series of vaccines and adults who can’t get vaccinated for medical reasons such as pregnancy or immune-system problems.

“The evidence is pretty clear,” said Lieu, “that parents who decline vaccines increase the risk of preventable disease not only in their children but also in other community members.”

Contact Lisa M. Krieger at 650-492-4098.