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Study shows vaccine-autism link unlikely

Infants are shown to rapidly metabolize the type of mercury used in the
preservative
thimerosal, still widely used in vaccines around the world.
By Thomas H. Maugh II, Los Angeles Times Staff Writer
January 31, 2008
New studies in infants show that the mercury used as a preservative in vaccines
is
cleared from the body at least 10 times faster than researchers had previously
believed,
a finding that casts further doubt on the theory that the preservative causes
autism.

Researchers had believed that the ethyl mercury in the preservative thimerosal
is
metabolized in much the same way as the methyl mercury found in fish and other
sources.

But the first study of ethyl mercury in children shows that levels of mercury in
the blood
are only a tenth as high as expected, and the toxic element is cleared out
rapidly,
according to a paper to be published Monday in the journal Pediatrics.

There is a "clear relationship" between the amount of mercury that must be in
the blood,
the length of time it must remain there, and the likelihood of it accumulating
in the brain
to cause damage, said Dr. Michael E. Pichichero of the University of Rochester
in New
York, the paper's lead author. "Now it's obvious that ethyl mercury's short
half-life
prevents toxic buildup from occurring. It's just gone too fast."

The bottom line, said Dr. William Schaffner of Vanderbilt University, who was
not involved
in the study, is that "this is yet another study added to the increasing stack
of studies
that are reassuring about thimerosal's safety."

But Isaac Pessah of the UC Davis MIND Institute pointed out that the researchers
had only
studied healthy children. They didn't address "the key issue of whether a subset
of kids
with metabolic disorders would handle it differently."

Like the authors, he also noted that they couldn't examine the brain and other
organs for
mercury accumulation.

Still, the findings should reassure parents of millions of infants around the
world who
receive vaccines with thimerosal even though it was eliminated from most
childhood
vaccines in the U.S. in 1999, Pichichero said. Removing thimerosal would raise
prices and
limit availability in poor countries.

Autism strikes as many as one in 167 children born in the U.S. Many parents link
the
increase in cases to past use of thimerosal in vaccines. The new study was
designed to
address those concerns.

It confirms previous findings of Pichichero and his colleagues in studies in
rhesus
monkeys and in a much smaller group of infants.

In the latest study, they examined 72 newborns, 72 2-month-old infants and 72 6-
month-olds at R. Gutierrez Children's Hospital in Buenos Aires, where thimerosal
is still
used in vaccinations.

They found that blood mercury levels spiked shortly after vaccination --
although they
remained much lower than levels of methyl mercury observed in other studies --
then
dropped, with a half-life of 3.7 days. The half-life of methyl mercury, in
contrast, is 44
days.

They also found that levels of mercury in the blood were about the same at
birth, at 2
months and at 6 months.

"That's super-reassuring evidence that you don't accumulate mercury, you get rid
of it,"
Schaffner said.

The researchers found no evidence of mercury in urine, indicating that the toxic
metal
was not coming into contact with the kidneys. Most of the mercury, they found,
was
eliminated through the feces.

Dr. Peter Hotez of the Sabin Vaccine Institute, who was not involved in the
study,
characterized it as "beating a dead horse."

"On the other hand, it is useful to know that ethyl mercury does not have the
same
metabolism as methyl mercury," he said.

The study was funded by the National Institutes of Health. The researchers said
they had
in the past been paid for consulting with vaccine manufacturers.

thomas.maugh@...