The people most likely to refuse to have their children vaccinated tend to be white, well-educated and affluent, researchers report.

A study published in the January issue of the American Journal of Public Health used California state government data on “personal belief exemptions,” or opting out of vaccinations for nonmedical reasons. From 2007 to 2013, the rate of vaccine refusal for personal belief doubled, to 3.06 percent…

In some suburban areas, rates of exemption were near 50 percent, and more than a quarter of California’s schools have measles immunization rates below the 92 to 94 percent required for herd immunity, the level of vaccination necessary to protect people who are not immune.