- WASHINGTON (Reuters) - There
is no proof that a mercury-containing preservative present in some vaccines
causes developmental disorders in children, but doctors should steer clear
of giving children vaccines made with the substance just to be safe, a
panel of experts said in a report on Monday.
- The report by a panel convened by the Institute of Medicine,
which provides advice on health issues to the U.S. government under a congressional
charter, focused on thimerosal, long used in some vaccines and other pharmaceutical
products to prevent bacterial and fungal contamination.
- The committee concluded that no evidence currently exists
proving a link between thimerosal-containing vaccines and autism, attention
deficit-hyperactivity disorder, speech or language delays, or other neurodevelopmental
- But the panel said it is ``biologically plausible'' that
some children's risk of one of these disorders could be increased by exposure
to mercury from vaccines containing thimerosal, which contains nearly 50
percent mercury by weight. The experts said existing evidence is insufficient
either to accept or reject the idea that thimerosal-containing vaccines
can cause these childhood disorders.
- Levels of mercury, which can harm the nervous system,
can build up in the human body with each exposure, whether from vaccinations
or other sources such as contaminated fish.
- Very few vaccines used in the United States still contain
thimerosal and many types of vaccines never contained it, the panel said.
But the committee recommended that, as a prudent precaution, vaccines that
contain thimerosal not be used when vaccines made without it are available.
- ``Most children in the United States being immunized
today and in the future are unlikely to receive a vaccine that contains
thimerosal,'' Marie McCormick, a professor of maternal and child health
at Harvard School of Public Health who headed the Institute of Medicine
committee, said in a statement.
- ``In those few cases where only supplies containing the
preservative are available, the vaccines should be administered rather
than foregoing immunization. While the health effects of thimerosal are
uncertain, we know for sure that these vaccines protect against real, proven
threats to unvaccinated infants, children, and pregnant women,'' McCormick
- The report was requested by federal health officials.
- PRECAUTIONARY STEPS URGED
- The committee recommended that U.S. policy-makers weigh
additional precautionary steps to reduce exposure to thimerosal. The panel
urged that government agencies and professional societies review their
policies about nasal sprays, eye drops and other products that contain
thimerosal and are used for infants, children and pregnant women.
- Thimerosal has been used in vaccines since the 1930s.
- But the three-in-one vaccine against measles, mumps and
rubella (also called German measles) never contained the preservative,
nor did the vaccines for chicken pox or polio.
- Several other vaccines recommended for children until
recently were made with thimerosal. The committee said these vaccines now
are made without it, but an unknown, probably small number of vaccine doses
remain on clinic shelves. They include vaccines for hepatitis B, diphtheria,
tetanus and pertussis (whooping cough), and haemophilus influenzae type
B (Hib), a form of bacterial meningitis.
- A few vaccines, including influenza vaccine given annually
during the viral flu season to adults and some children, still are manufactured
- Thimerosal also remains in use in many other countries.
- Two years ago, the federal government and leading medical
organizations urged new limits on mercury exposure of infants and young
children -- a move that instigated the development of routine childhood
vaccines made without thimerosal.