By Lisa Esposito
MONDAY, Oct. 31 (HealthDay News) -- By signing an affidavit that says "all or some immunizations are contrary to my beliefs," California parents can bypass requirements that their children be fully immunized before attending school, and new research indicates that many are choosing to do so.
The new study shows that at some "hot spot" schools, one out of every five kindergarten students is now going unvaccinated by parental choice -- putting not only these kids at risk of preventable infectious diseases, but also other children at the school.
These are schools "where we might be concerned that 'herd immunity' has been compromised," warned lead study author Alison Buttenheim, an assistant professor in family and community health at the University of Pennsylvania School of Nursing.
"Herd immunity is the protection offered to unimmunized people when most people are immunized or otherwise unsusceptible," she explained. "For example, our herd immunity against measles protects infants, up to age 1, who are too young to receive the MMR [measles, mumps, rubella] shot."
Buttenheim added that "schools are an important site of exposure for children. All of our measures point to increasing exposure to intentionally unvaccinated children among California kindergarteners, a worrisome trend."
The new finding was slated for presentation Monday at the annual meeting of the American Public Health Association in Washington, D.C. It comes on the heels of recent U.S. Centers for Disease Control and Prevention (CDC) findings that with more unvaccinated kids, the United States is now experiencing its largest measles outbreak in 15 years. Experts have also blamed a recent resurgence in cases of whooping cough (pertussis), especially in California, on declining child vaccination rates.
Twenty states currently allow "personal belief exemptions" when it comes to child vaccinations: Arkansas, Arizona, California, Colorado, Idaho, Louisiana, Maine, Michigan, Minnesota, New Mexico, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Texas, Utah, Vermont, Washington and Wisconsin.
In the new California study, researchers analyzed state health department figures on personal belief exemptions among kindergartners. Some schools had much larger proportions of these children than others, raising concerns that clusters of unvaccinated children might lead to outbreaks of diseases like measles, mumps and rubella.
The researchers deemed as "hot spots" schools where more than 20 of 100 children claimed personal belief exemptions.
The researchers found that in 2010, for every 100 children in a California kindergarten, 2.3 had bypassed immunization due to one or more personal belief exemptions. These exempted children tended to cluster in certain schools, typically attending schools where an average of almost 16 of every 100 of their peers also claimed exemptions.
In some schools, more than one in five kindergartners had parental exemptions for vaccination, the study found. More than 7,000 kindergarteners across California attended these schools, including 2,700 who were exempted.
"This looks like an important study, one that's consistent with what we've been learning about philosophical and personal exemptions," said Dr. Lance Rodewald, director of the immunization services division at the CDC. "Studies done in the past show that the easier it is to get an exemption, the more likely a child will get one. Other studies show that the easier it is to get an exemption, the lower the coverage levels."
Rodewald said climbing exemption rates can have far-reaching consequences -- even for children who get vaccinated.
"It does matter for non-exempted children. While with measles vaccination, one dose gives 95 percent protection, the pertussis [whooping cough] vaccine is very good but not perfect. Pertussis wears off over time. [So] even if a child was vaccinated, it's still possible to get pertussis," Rodewald explained. "With a lot of exempters, you can attract an outbreak. We're seeing a lot of pertussis right now."
Buttenheim agreed. "Making sure your children are up to date on the recommended immunization schedule is an easy, safe and effective way to protect your child's health," she said. "However, no vaccine is 100 percent effective. Your vaccinated child still has a very small -- but not zero -- probability of contracting a vaccine-preventable disease if exposed."