SACRAMENTO, Calif. — 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 forego 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.



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.



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.



Bibi Reber, whose children attend the Waldorf-inspired Greenwood School in Mill Valley, had her children vaccinated only for what she sees as the deadliest diseases. Greenwood has a 79 percent opt-out rate among its kindergartners.



"I don't think dirt or getting sick makes you a weak person; your immune system needs to work with things," said Reber, whose children attend the Greenwood School in the San Francisco Bay area town of Mill Valley. "We certainly don't want to go back to having polio, but on the other hand, I don't think we need to eradicate all the childhood diseases



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.



State Assemblyman Richard Pan, a pediatrician, who sponsored the bill, said he believes private school parents are more apt to mistakenly believe that the vaccinations themselves could be more dangerous than the diseases.



"In private school, these are people who have money, who are upper middle-class, and they are going on the Internet and seeing information and misinformation," said Pan, D-Sacramento.



Increasing immunization rates for this population is critical to controlling the outbreak of diseases, he said. "Have you ever seen a child cough themselves to death? It's not pleasant," he said.



Those who choose not to vaccinate their children see the legislation as meddlesome and unnecessary.



"It's making an extra appointment and paying extra money to go in there and essentially get permission to do what I feel is right for my family," said Dawn Kelly, who sends her unvaccinated 5-year-old son and partially vaccinated 9-year-old son to Monarch Christian School in the Los Angeles area.



Like many parents who refuse some or all immunization shots, Kelly worries her children's immune system could be overwhelmed by getting too many vaccines at once.



Melani Gold Friedman, president of the parent association at Highland Hall Waldorf School, is concerned with what the legislation means for families who normally consult with acupuncturists, holistic healers or other alternative practitioners.



"The bill has an assumption that everyone's seeing one particular kind of doctor, but the people who are opting out, chances are they're not seeing that kind of doctor," she said.



Vaccination opt-out rates nationwide have been creeping up since the mid-2000s, spurred in part by the belief the battery of vaccinations routinely given to infants could lead to autism. Several major studies have discredited that idea.



Parents are allowed to forego vaccines for philosophical reasons in California and 19 other states. Of those, only Washington requires parents to consult with a physician. And, in California, there's no difference between private and public schools when it comes to what's required for parents to opt out — they simply sign a document. The state recommends that kindergarteners receive five vaccine progressions, including protections against Polio, Hepatitis B and Measles



Politicians and public health experts across the nation are focusing more attention on childhood immunizations, driven by a re-emergence of diseases like whooping cough. The U.S. is in the midst of what could be its worst year for that disease in more than five decades, with nearly 25,000 cases and 13 deaths.



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's more than doubled since 2004, to 2,228 kindergartners in last year's state survey. While the overall rate of full immunization among kindergarteners hovers around 91 percent, places where the opt-out rate is greater could pose a risk for outbreak.



In 2008, East Bay Waldorf School in El Sobrante closed temporarily after whooping cough sickened more than a dozen students, eight of them kindergartners. The San Francisco Bay Area school had a vaccination rate of less than 50 percent.



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.



The AP analysis found 20 of the 25 California private schools with the highest opt-out rates are "Waldorf schools," a loose association of institutions founded on the teachings of 19th-century philosopher Rudolf Steiner. He favored a holistic approach to education and medicine and thought childhood illnesses could be beneficial.



Officials at these schools would not comment about Pan's bill but say they trust parents to make the best decisions for their children's health.



"Parents who are brave enough to say, 'No, that's not the right thing,' should be supported," said Patrice Maynard, spokeswoman for the Association of Waldorf Schools of North America.