At this point, it’s well documented that affluent, educated white communities are behind the surge in unvaccinated kids—and by extension the increase in vaccine-preventable diseases, including measles and whooping cough (pertussis). But there are few studies that dig into the detailed demographics of those unprotected younglings, leaving health experts at a loss for how to target strategies to combat anti-vaccination myths and fears in the specific groups that need it most.

Some help may come in the form of a new analysis of Californian kindergarteners who obtained personal belief exemptions (PBE) from vaccination between 2007 and 2013. Researchers found, as expected, that those kids were most likely to be white, come from high-income homes, and were frequently enrolled in private school. Although kids in this group tend to have parents with lots of schooling, high-education levels among family did not independently track with the rise in vaccine opt-outs.

“Our results call into question the reported link between high-PBE communities and higher average educational attainment,” the study's authors concluded. These findings, published in the American Journal of Public Health, suggest that sharing more scientific data on vaccine safety and the consequences of vaccine-preventable illnesses may not be enough to combat anti-vaccination trends.

Some trends came through clearly in the new analysis, led by Y. Tony Yang of George Mason University. In assessing the demographic data, the researchers found that vaccine refusal due to personal beliefs doubled from 2007 to 2013, hitting 3.06 percent. Over that time period, more than 17,000 children attending more than 6,000 schools in California had opted out of normal vaccination schedules.

In more than 25 percent of schools in the state, the kindergartener immunization rate for measles has fallen below the 92-to-94 percent threshold that is recommended for maintaining herd immunity. That means that a quarter of California schools may not have enough vaccinated children to keep from having an outbreak, possibly endangering kids who are too young or medically unable to get vaccinated.

With a clearer look at the demographics, the authors suggest that public health experts trying to reverse the trend may need to place more emphasis on dispelling a notion among privileged whites that protective parenting can replace immunization.

The authors also saw some good news in the data. Many efforts to boost vaccination rates have focused on making exemptions harder to get. This had led some health experts to worry that new hurdles will be a disproportionate burden for hardworking, lower-income people who need to seek medical exemptions. But, the authors conclude, “our study and others suggest that such persons may be relatively uncommon among PBE seekers.” Thus, more restrictions on exemptions may be effective, they write.

In June, California passed a law that eliminates personal belief exemptions among children attending school. The law takes effect January 1.

American Journal of Public Health, 2015. DOI: 10.2105/AJPH.2015.302926 (About DOIs).