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Vaccine study findings fuel debate over autism
SANDY KLEFFMAN, "Vaccine study findings fuel debate over autism",
Kansas City Star, March 22, 2006,
A new UC Davis study links a mercury-containing preservative once
prevalent in many children's vaccines to immune system dysfunction in
The findings are sure to heighten the debate over whether vaccines play
a role in causing autism, especially since there is growing evidence
that many autistic children have irregular immune systems.
The researchers released their results with an abundance of caution,
stressing that numerous questions remain about thimerosal's effect on
humans and its relationship, if any, to the recent rapid rise in the
numbers of autistic children.
The study is a road map for future investigations of the effect mercury
from a variety of sources has on developing immune systems, said senior
author Isaac Pessah, a UC Davis toxicologist.
"This is a clue, a lead - I hope it will stimulate a lot more
research," said Cindy Lawler, a program administrator for the National
Institute of Environmental Health Sciences, which funded the study with
the UC Davis M.I.N.D. Institute.
Although no longer used widely in children's vaccines in the United
States, thimerosal remains in some flu vaccines and over-the-counter
The Davis researchers removed dendritic cells from mice, then analyzed
how thimerosal affected those cells in culture dishes. A dendritic cell
acts as a sentry, helping to marshal the body's immune system against
invading viruses or bacteria.
One dendritic cell can activate as many as 300 T-cells, the white blood
cells that help find and kill attacking agents.
Among the study's findings:
· Thimerosal dramatically altered dendritic cells by garbling their
· At lower levels, it caused dendritic cells to secrete abnormal
levels of cytokine, a substance that initiates inflammatory responses.
· At higher levels, it caused the death of dendritic cells,
preventing them from maturing and activating T-cells.
· Even extremely small amounts of thimerosal interfered significantly
with dendritic cell function after a few minutes of exposure.
· Immature dendritic cells were particularly sensitive to thimerosal.
Thimerosal has been used as a preservative in some vaccines and other
pharmaceutical products since the 1930s.
Manufacturers use it to prevent fungal and bacterial contamination in
multidose vials. It isn't needed in individually packaged doses, a more
Manufacturers began to remove thimerosal from children's vaccines in
1999 when the American Academy of Pediatrics and the U.S. Public Health
Service urged them to do so as a precautionary measure.
The recommendation came after the Food and Drug Administration
determined that children who received the full set of recommended
immunizations could accumulate doses of mercury exceeding Environmental
Protection Agency guidelines.
Today, most children's vaccines in the United States contain only trace
amounts of the preservative. The one exception is the flu shot, which
is available with and without thimerosal, although the thimerosal
version is much more prevalent.
The preservative remains in some ear drops, nose drops, skin creams and
cosmetics, as well as adult diphtheria and tetanus vaccines.
Anyone who takes a hard look at thimerosal wades into roiling political
waters. While federal health officials insist it is safe, several
thousand parents of autistic children have sued pharmaceutical
companies, blaming them for causing their children's disorder.
Congressional leaders have entered the fray, arguing about whether to
grant pharmaceutical companies immunity from such lawsuits.
Pessah made sure Tuesday he avoided aligning with either side in the
debate. "We're just trying to do the best science we can," he said.
Many questions remain, said Pessah, who directs the UC Davis Children's
Center for Environmental Health and Disease Prevention.
"I want to be clear that I'm not saying thimerosal is causing autism,"
The study doesn't reveal whether thimerosal would have the same effect
in a mouse's body as in a petri dish, or whether it affects human cells
the same way it does mice cells, he noted.
It also is not known whether immune system dysfunction leads to autism.
Despite the questions, the findings will intrigue many parents of
"It is another step in our understanding," said Rick Rollens, the
father of an autistic boy and a co-founder of the M.I.N.D. Institute.
"The thing that's most exciting to me about this is that science is now
listening to us and is pointed in what we believe is the right
The next step for researchers, Pessah said, is to test the effect of
thimerosal and other forms of mercury on human dendritic cells.
UC Davis will gather such cells from 350 children enrolled in an
ongoing autism study.
A complementary UC Davis study is analyzing whether autism is actually
several disorders lumped into one category. Many experts believe it has
a variety of causes.
California will ban thimerosal from vaccines given to expectant mothers
and children younger than 3 years old beginning this July.
Although some parental groups have urged the CDC to recommend removal
of the preservative from the flu vaccine, the CDC has declined to do
Manufacturers do not produce enough of the thimerosal-free children's
version for everyone who needs it, said CDC spokeswoman Lola Russell.
Reach Sandy Kleffman at 925-943-8249 or .
THIMEROSAL AT A GLANCE
· Most health experts recommend full vaccinations for children. Only
trace amounts of thimerosal exist in most children's vaccines today.
· The one exception is the flu shot, which is available with and
without the preservative. Parents who want the thimerosal-free version
should request it when their children receive shots.
· Thimerosal is in some ear and nose drops, creams and other
over-the-counter pharmaceutical products.
· Thimerosal remains in some adult diphtheria and tetanus vaccines.
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