Mercury from vaccines seems to disappear rapidly from the blood,
returning to pre-vaccination levels in one month, according to a small
study of children in Argentina.
The findings bolster the argument that a mercury-based vaccine
preservative does not cause autism in children, although it is unclear
from the study whether some mercury may linger elsewhere in the body.
The research addresses an unanswered question about the safety of
thimerosal, a preservative that has been eliminated from most vaccines, and breaks down as ethyl mercury in the body. It is still
used in some countries, including Argentina.
The new findings suggest that methyl mercury and ethyl mercury are
very different and that the removal of thimerosal from vaccines may
have been over-cautious.
"The study supports the decision by the World Health Organization to
continue to permit thimerosal to remain in vaccines for the world's
children," said study co-author Dr Michael Pichichero of the
University of Rochester in Rochester, New York. He said thimerosal
vaccines are cheaper to produce and therefore more accessible to much
of the world.
In the US-funded study, blood samples were taken from 216 healthy
babies before and after they got vaccines containing the preservative
thimerosal. Blood levels of mercury were highest shortly after the
babies were vaccinated and fell to pre-vaccination levels within a few
"The amount found in the blood was about one-tenth of that predicted
in the late 1990s and the length of time it stays in the blood is
one-tenth of that predicted," Pichichero said.
Mercury levels also were measured in the babies' stools and urine.
In the stool samples, the levels were highest after vaccination and
also fell, but more slowly than blood levels. There was no significant
amount of mercury in the urine.
The authors could not determine what happened to all the mercury
after it left the blood. All the infants gave samples twice: before
vaccination and at one other time, ranging from 12 hours later to 30
Findings released early
The study will be published in the February issue of the journal
Pediatrics. The medical journal released the findings early because of
a controversy surrounding a new US TV series premiering Thursday, which
features a lawyer who argues in court that a flu vaccine made a child
The journal is published by the American Academy of Pediatrics,
which on Monday called on ABC to cancel the first episode of the
series "Eli Stone", saying that it perpetuates the myth that vaccines
can cause autism.
Autism is a complex disorder featuring repetitive behaviours and poor
social interaction and communication skills. Scientists generally
believe that genetics plays a role in causing the disorder. A theory
that thimerosal is to blame has been repeatedly discounted in
Pichichero said he has received research grants and served as a
consultant to several vaccine makers, but said there was no industry
involvement in the new study. He is an unpaid consultant to the WHO on
vaccines. – (Sapa-AFP)
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