Dec. 3, 2002 -- A federally funded study offers
reassurance to those who are concerned about the health risks of
vaccines containing the preservative thimerosal. Researchers found that
blood mercury levels in vaccinated infants were well below those
considered safe and that mercury was eliminated from the body much
faster than expected.
The findings suggest that government health officials
may have acted prematurely in recommending the removal of thimerosal
from vaccines in the summer of 1999. The move came in response to public
fears that the mercury in the preservative may be linked to an increase
in autism, asthma, and several other childhood diseases. Vaccines
containing thimerosal are no longer given to children in the U.S., but
the preservative is still widely used in vaccines given to children in
other countries. Removal of the preservative has reportedly raised costs
of producing, storing, and shipping vaccines.
"Our most important finding was that not a single child
had a blood mercury level which exceeded the most stringent safety
standards -- those set by the Environmental Protection Agency [EPA],"
lead researcher Michael E. Pichichero, MD, tells WebMD. "We also showed
that the mercury in vaccines is eliminated from the body six to seven
times faster than has been predicted."
In the study, reported Nov. 30 in The Lancet,
Pichichero and colleagues from New York's University of Rochester
Medical Center examined mercury levels in the blood, urine, and stool of
40 infants given vaccinations containing thimerosal and 21 infants who
received thimerosal-free vaccines. All infants received
diphtheria-tetanus-acellular pertussis (DtaP) and hepatitis B vaccines,
and some were also given an Haemophilus influenzae type B
vaccine. These immunizations are typically given to children at the ages
of 2 months, 4 months, and 6 months.
All of the children were found to have mercury levels
below the EPA's public safety limit of 5.8 nanograms per milliliter (ng/mL).
Most had blood mercury levels ranging from 1 to 2 ng/mL, and the highest
level found was 4.11 ng/mL.
The children eliminated half of the vaccine-related mercury in
their stools within six to seven days of inoculation, instead of the 45 days
that had been predicted by previous studies. This suggests that typical
vaccination schedules are safe, Pichichero says.
"Vaccines are usually given to infants two months apart, and our
findings suggest that by 60 days there is virtually no mercury left in the
body," he says. "So there is no cumulative effect."
Immunization expert Neal Halsey, MD, who has been outspoken in
calling for increased vaccine safety research, calls the National Institute of
Allergy and Infectious Diseases-funded study a good start.
"This is a good study, and it helps us to understand the
metabolism of ethyl mercury associated with thimerosal," says Halsey, director
of the Institute for Vaccine Safety at Baltimore's Johns Hopkins Bloomberg
School of Public Health. "But one thing we don't know from this study is what
the peak levels of mercury are shortly after vaccination."
The University of Rochester researchers hope to address this
question in a similar study of 200 children now under way in Argentina. But
Halsey says the definitive answer to the safety question is at least several
years away. That is when results are expected from a separate government
follow-up study of children exposed to differing levels of thimerosal.
"Everyone has a small amount of mercury in their body from
different exposures," he tells WebMD. "The question is what level is associated
with harm in young children."
SOURCES: The Lancet, Nov. 28, 2002 •
Michael E. Pichichero, MD, professor of microbiology and immunology, pediatrics,
and medicine, University of Rochester Medical Center, New York • Neal A. Halsey,
MD, professor of international health and pediatrics; director, Institute for
Vaccine Safety; director, Division of Disease Control, Johns Hopkins Bloomberg
School of Public Health, Baltimore, Md.
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