|
 Vaccine
Additive Linked to Brain Damage in Children
Mercury-based preservative tied to autism, ADHD, U.S.
researchers say.
by Sharon Kirkey, CanWest News Service, February 5, 2004
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After assuring
parents that additives in vaccines don't cause brain damage,
scientists have found what they believe could be a "smoking gun"
linking these additives to autism and attention-deficit
hyperactivity disorder in children.
In a study that was rushed to print on-line today, two months
ahead of its scheduled publication in the journal Molecular
Psychiatry, U.S. researchers have discovered an apparent link
between thimerosal, a controversial mercury-based preservative
once commonly used in childhood vaccines, to an increased risk
of neurological disorders such as autism and ADHD.
While most vaccines distributed in Canada have been thimerosal-free
since the early 1960s, the preservative was used in the annual
flu shot that doctors recommended this year for even healthy
children.
In tests on human brain cells, researchers found two natural
chemicals -- one compound that stimulates cell growth and also
dopamine, which transmits nerve signals -- are both key to a
process in the brain called methylation. Methylation helps DNA
work properly and is crucial to the normal development of the
brain.
The team found thimerosal, ethanol and the metals lead and
mercury all interfere with methylation. What's more, thimerosal
did so at doses 100 times lower than a child would receive after
a single shot with a thimerosal-containing vaccine.
"It was by far the most potent," said investigator Dr. Richard
Deth, a professor of pharmacology at Northeastern University in
Boston.
He said the study, which also involved researchers from Johns
Hopkins University, the University of Nebraska and Tufts
University in Boston, could account for the rising rates of
autism since the early 1980s, when more thimerosal-containing
shots were added to a child's vaccine schedule
A recent review of vaccine-related "adverse events" in the U.S.
found a "significant correlation" between shots containing
thimerosal and autism, the researchers report.
But one of Canada's leading experts in vaccination says large
studies have repeatedly failed to find any association between
brain damage and vaccines that do, or don't, contain thimerosal.
"What [the researchers] are doing in the test tube may or may
not have any relationship to what happens in the body," added
Dr. Ronald Gold, professor emeritus of pediatrics at the
University of Toronto and author of Your Child's Best Shot: A
Parent's Guide to Vaccination. He says there's no evidence that
the low doses of thimerosal researchers tested would even cross
a child's blood-brain barrier.
Dr. Perry Kendall, B.C.'s chief health officer, was also
skeptical of the study, although he said he had not yet had a
chance to read it.
He said there have been several studies that make weak links
between autism and vaccines, but none has been definitive.
"I think that the link between thimerosal and autism has been
studied quite extensively to date," he said. "And I don't think
there's any convincing evidence on the population basis that
vaccination is underlying the increase in autism."
Kendall said he was not aware, however, of any other studies
that make a link between vaccines and ADHD.
In B.C., thimerosal is still used in the hepatitis B vaccine
that is given to Grade six students, as well as the annual flu
shot, he said.
Before the early '90s, most causes of autism were believed to
have a strong genetic component, and symptoms surfaced soon
after the child was born.
But, a newer, and more common form of the disease is known as
regressive autism, in which children appear to be developing
normally, but then suddenly regress. "They lose functions they
had before, such as early speech," Deth says. "Parental
anecdotes and clinical reports have suggested it happened during
periods of high vaccine exposure."
"Up to now, people have said the cause, or causes of autism, are
unknown. Our work isn't final in any sense at all, but it seems
to point to this biochemistry as a potential, or even primary
cause, of autism."
Thimerosal had been used to prevent the growth of bacteria or
fungi in multi-dose units of vaccines for diseases such as
hepatitis and diphtheria, pertussis (whooping cough) and
tetanus, or DPT.
As of March 2001, all vaccines for routine immunization of
children in Canada have been available without thimerosal. But
the annual flu shot, which is given to children over six months
of age -- contains the preservative. And thimerosal is still
found in larger, multi-dose vaccines shipped to Third World
countries.
Dr. Laszlo Palkonyay, medical-scientific adviser for
Quebec-based flu vaccine maker Shire Biologics, said a study
published in the journal Pediatrics last September, which was
based on a registry of all psychiatric admissions in Denmark
between 1971 and 2000, found no trend toward an increase in
autism rates during the period thimerosal was used in vaccines
in that country. In fact, he said the incidence of autism
increased after the preservative was removed from vaccines in
1990.
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