Norcal’s Under-Immunization Problem
A new study by Kaiser Permanente has identified clusters of underimmunized children in Northern California that took even researchers by surprise.
The study, part of a larger look at vaccination preference undertaken by the Patient-Centered Outcomes Research Institute, was released this week as a measles outbreak in California continues to grow, prompting one Southern California county to order some households to self-quarantine their school-age children.
Kaiser’s study was based on its own electronic medical records system. Vaccination records of more than 154,000 of Kaiser pediatric health plan enrollees born between 2000 and 2011 were examined. Spatial analysis software determined whether enrollees were under-vaccinated, meaning they received fewer than the 17 injections required during their first two years of life to prevent 10 different diseases, including measles, mumps, hepatitis, diphtheria, tetanus and pertussis, among others.
Some parents in recent years have eschewed vaccinating their children, fearing that preservatives or other chemicals in the vaccines are linked to autism, a conclusion that remains scientifically unfounded.
According to lead researcher and Kaiser pediatrician Tracy Lieu, M.D., there are clusters of underimmunization in the East Bay, Sonoma and Napa Counties, eastern Sacramento, northern San Francisco and southern Marin County and an isolated area of Vallejo. Those regions had an under-immunization rate between 2009 and 2012 that ranged from 17.5% to 22.7%, compared to an 11% statewide rate of under-immunized children.
The phenomenon is typically linked to a practice known as “shot-limiting,” wherein parents restrict vaccinations to no more than two during a pediatric care visit. White households were far more likely to have under-immunized children than any other ethnic group.
"This research confirms anecdotal reports of underimmunization clusters," Lieu said. “In addition, we found clusters in places we hadn't anticipated."
According to Kaiser spokesperson Janet Byron, “the cluster in southern Marin County has been fairly well documented based on personal belief exemptions....so regionally the others may have been less anticipated.” She added that there was a sub-community in east Sacramento that was “vaccine-hesitant.” Like Marin County, eastern Sacramento contains a hub of highly educated and affluent households. However, the Kaiser study was not designed to determine what may be influencing parents not to immunize their children.
The study also identified areas where parents refused all or most vaccinations. Those included the East Bay, Marin and southwest Sonoma Counties, northeastern San Francisco, northeastern Sacramento County, a small area just south of Sacramento, and Roseville. Vaccine refusal rates in the clusters ranged from 5.5% to 13.5%, compared to just 2.6% statewide.
Health experts generally believe that if a community-wide vaccination rate dips below 92%, the strength of herd immunity erodes, raising the risk of outbreaks of preventable diseases.
"Everyone in the Kaiser healthcare 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."
Meanwhile, the California Department of Public Health announced on Wednesday that the number of Californians with measles had risen to 59, the largest number in years, although the Los Angeles Times reported 67 cases as of Wednesday evening.
Of those, 44 cases have been traced to exposures that occurred at the Disneyland Resort in Anaheim last month. The CDPH also reported several secondary cases of measles -- cases that were spread by the Disneyland cases after they left the park. No deaths or hospitalizations have been reported.
Altogether, at least 28 of the cases involved unvaccinated children or adults. In Orange County, public health officials ordered children who had not been vaccinated for measles to stay away from their schools for three weeks.
