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
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
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."
So why the rise in parents opting not to vaccinate their
"Parents choose not to vaccinate for many reasons," Buttenheim said. "To generalize across this diverse group, they perceive the risks associated with vaccines to be greater than the risks associated with vaccine-preventable diseases. While there is a very strong scientific consensus that this calculation is not correct, we cannot simply ignore or dismiss parental vaccine hesitancy."
One big contributor has been the (now discredited) notion that
the measles-mumps-rubella shot might raise autism risk. In 1998, a
small but widely publicized study appeared to link childhood MMR
vaccination to nine cases of autism. The study appeared in the
The Lancet, which retracted the study in 2010. In January of this year, an investigation by another leading British journal, BMJ, denounced the findings as deliberately fraudulent. But the damage was done.
That, and worries about thimerosal, a mercury-containing
preservative once widely used in vaccines, has contributed to
Not all kids with personal belief exemptions are left fully
unvaccinated, Buttenheim noted. "We are only able to say whether
they have exemptions from one or more vaccines. Children we observe
as having personal belief exemptions may have not done, for example
[diphtheria, tetanus and pertussis] vaccination, but may be up to
date on MMR."
"In general, parents do value vaccines but exemptions do happen," said Rodewald, who is a pediatrician. "Parents have a lot of questions and they want to make sure that vaccines are effective and safe. It's important that health professionals like pediatricians, nurse practitioners and school nurses be able to answer questions for parents so they can make informed decisions; decisions of knowledge and strength."
Because the new study was presented at a medical meeting, the
data and conclusions should be viewed as preliminary until
published in a peer-reviewed journal.
The U.S. National Institute of Allergy and Infectious Diseases
herd immunity works.
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