Created By: Riley Quijano
In the late 1990s,  some researchers started raising concerns over the
amount of thimerosal -- a mercury-containing preservative -- found in
many children's vaccines. Although thimerosal had been used as an
anti-contamination agent for decades, until 1991 the
diphtheria-tetanus-pertussis (DTaP) vaccination was the only
thimerosal-containing shot recommended for infants
and children. The hypothesis: As more thimerosal-containing vaccines
like hepatitis B and Hib were added to the recommended schedule,
 researchers worried that babies were receiving too much of the chemical
in too short a timeframe, which could potentially impact brain
To understand more about thimerosal safety, a brief chemistry/history
lesson is in order.  Thimerosal was removed from most vaccines by 2001
because researchers worried that children were being exposed to too-high
levels from receiving multiple vaccinations in a short timeframe.
 But this decision was based on what levels were considered safe
for methyl mercury -- the kind in fish, which is structurally very
different from the ethyl mercury found in thimerosal. Although
scientists suspected that thimerosal was much safer than methyl mercury,
they decided to remove it anyway, just to be super-careful.
 Now, new research published in the journal Pediatrics
shows that babies excrete thimerosal too quickly for it to build up to
dangerous amounts. In the study, researchers tested the blood mercury
levels of Argentinean babies after they received routine childhood
vaccinations (thimerosal is still used as a vaccine preservative there).
They found that infants
expel thimerosal about 10 times faster than fish mercury -- so rapidly
that it can't accumulate in the body between vaccine doses.
"This study helps to debunk a crucial basis of the
autism-vaccines theory, which held that babies were getting so many
thimerosal-containing shots that the chemical would build up in the
bloodstream and eventually cross over to the brain, where it could
theoretically impact development," says study author Michael Pichichero,
MD, a professor of microbiology/immunology and pediatrics at the
University of Rochester Medical Center. "But thimerosal leaves babies'
bodies way too quickly for that to happen, which just adds more proof
that this theory is extremely unlikely."
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