SACRAMENTO -- Parents who send their children to private schools in California are much more likely to opt out of immunizations than their public school counterparts, an Associated Press analysis has found, and not even the recent re-emergence of whooping cough has halted the downward trajectory of vaccinations among these students.
The state surveys all schools with at least 10 kindergartners to determine how many have all the recommended immunizations. The AP analyzed that data and found the percentage of children in private schools who forgo some or all vaccinations is more than two times greater than in public schools.
More troubling to public health officials is that the number of children entering private schools without all of their shots jumped by 10 percent last year, while the opt-out rate held steady in public schools for the first time since 2004.
Public health officials believe that an immunization rate of at least 90 percent in all communities, including schools, is critical to minimizing the potential for a disease outbreak. About 15 percent of the 1,650 private schools surveyed by the state failed to reach that threshold, compared with 5 percent of public schools.
There were 110 private schools statewide where more than half the kindergartners skipped some or all of their shots, according to AP's analysis, with Highland Hall Waldorf School in Northridge -- where 84 percent opted out -- topping the list.
A number of Bay Area private schools had kindergarten immunization rates far lower than 90 percent, though in some cases the numbers are so small that one family's decision can cause a large swing in the percentage. At Grand Lake Montessori in Oakland, with a rate of just 71 percent, three children -- about 21 percent of the kindergarten class -- received waivers for personal reasons. At Valley Montessori in Livermore, eight kindergartners, or 19 percent, didn't receive all of their shots.
Parents cite a variety of reasons for not immunizing their children, among them: religious values, concerns the shots themselves could cause illness and a belief that allowing children to get sick helps them to build a stronger immune system.
Likewise, there's no single explanation that accounts for why so many more parents who send their children to private schools apparently share a suspicion of immunizations.
Last winter, several classrooms at the Waldorf School of the Peninsula's two campuses in Los Altos and Mountain View experienced a chickenpox outbreak. The school worked with Santa Clara County public health officials and followed the requested safety protocol, said school administrator Stephanie Rynas.
"Had we been asked to, we were prepared to ask all families who opt out (of vaccinations) to be excluded from bringing their children to school during the course of the outbreak," she said.
Rynas said the proportion of vaccinated students at her school has remained roughly constant in recent years. Contacted over the weekend, she didn't have precise numbers.
"We certainly take student health very seriously. It's not an issue that the school per se takes a stand on. We follow the law and we report and we try to be diligent in our communications with parents and record-keeping, and to respond if needed."
At Ecole Bilingue, a bilingual school in Berkeley with a vaccination rate of 75 percent, parents most commonly opt out of the Hepatitis B and the MMR vaccines, said Jennifer Monahan, the school's communications manager.
"We don't give our families instructions one way or the other," Monahan said. "It's their personal choice. That's the way we look at it."
Saad Omer, a professor of global health at Emory University in Atlanta who has studied vaccine refusal in private schools, surmised more private school parents are wealthy and have the time to spread five shots over a series of years and stay home should their child get an illness like chickenpox. Neal Halsey, a professor of pediatric infectious diseases at the Johns Hopkins University, said parents who choose private schools are likely to be more skeptical of state requirements and recommendations.
Public health officials say that, regardless of why parents choose not to vaccinate their children, the result is the same: an increased risk of an outbreak of whooping cough or other communicable diseases.
"We're very concerned that those schools are places where disease can spread quite rapidly through the school and into the community, should it get introduced," said Dr. Robert Schechter, medical officer with the Immunization Branch of the California Department of Public Health.
That's what prompted the Legislature to approve a bill requiring parents to discuss vaccinations with a pediatricians or a school nurse before they can opt out. Gov. Jerry Brown has until the end of September to sign or veto it.
After whooping cough reached epidemic levels in California in 2010, the state took action, embarking on a public information campaign and increasing the availability of vaccines. A law was passed requiring booster shots for older students.
Yet the opt-out rate continued climbing in private schools. It has more than doubled since 2004, to 2,228 kindergartners in last year's state survey. While the overall rate of full immunization among kindergartners hovers around 91 percent, places where the opt-out rate is greater could pose a risk for outbreak.
In 2008, Waldorf School in El Sobrante closed temporarily after whooping cough sickened more than a dozen students, eight of them kindergartners. The school had a vaccination rate of less than 50 percent. Last year, only 27 percent of kindergartners had up-to-date vaccinations; 68 percent were opted out by their families for personal reasons.
State health officials are tracking the divergence of opt-out rates in private and public schools, but are not planning any studies or outreach efforts targeting this pupil population. The state is conducting a general education campaign to boost vaccinate rates.
Mercury News staff reporter Sharon Noguchi contributed to this story.
A look at the 15 California private school campuses with the highest vaccine opt-out rates among kindergartners:
-- Associated Press