Studies Find No Evidence That Vaccines Inflate Risk Of Autism
By Rob Stein - Washington Post
Scientists cast new doubt yesterday on suspicions that vaccines
increase the risk for autism, saying large studies conducted in
Denmark, Britain and the United States have failed to find a link
between the childhood shots and the brain disorder.
Other researchers, however, questioned the findings and presented
evidence they said supported the theory that mercury used as a
preservative in some vaccines may increase the risk for autism in
at least some children.
The conflicting research came at a day-long meeting sponsored by
the Institute of Medicine (IOM), an arm of the National Academy
of Sciences, which is investigating a possible link between
vaccines and autism at the request of the federal Centers for
Disease Control and Prevention in Atlanta.
Autism is a poorly understood disorder marked by a variety of
symptoms, most of them behavioral, such as difficulty interacting
socially and repetitive, sometimes self-destructive actions. The
number of children diagnosed with autism in the United States has
been increasing sharply. Although part of the increase is
believed to be the result of a broadening of the definition of
autism to include milder symptoms, that does not appear to
explain all of it.
Some researchers, advocates and parents of autistic children
blame childhood vaccines, which are administered at about the
same time that autism symptoms often appear. Suspicion has
focused on a mercury-containing compound known as thimerosal,
used as a preservative in some vaccines, which some suspect may
cause brain damage in certain genetically susceptible children.
Thimerosal has been phased out of most vaccines currently
available in the United States, but it is still used in some. It
is widely used in developing countries.
An IOM committee concluded in 2001 that there was insufficient
evidence that vaccines increased the risk for autism, but that
more research was needed because it was biologically plausible.
In the meantime, fears have lingered, and some public health
experts are alarmed that increasing numbers of parents may be
unduly discouraged from getting their children vaccinated against
what can be life-threatening childhood diseases, such as measles.
Since the 2001 report, a number of studies have examined the
issue, with many finding no association. Many of those studies
were presented yesterday to the IOM committee, including the
largest to date, a Danish study involving nearly 500,000 children
published in September.
In another, yet-unpublished study conducted for the World Health
Organization, Elizabeth Miller of the Communicable Disease
Surveillance Centre in London examined data collected about more
than 103,000 British children born between 1988 and 1997 who
received the thimerosal-containing vaccines at 2, 3 and 4 months
"Overall, there's no evidence of an increased risk for
developmental problems, including autism, from [thimerosal]
exposure in vaccines given in the U.K. in infancy," Miller told
Robert L. Davis of the University of Washington presented similar
findings from a study involving 223 children born between 1992
and 1998 who received care at two health maintenance
organizations in the Seattle area. "There is no evidence here for
an increased risk for autism," Davis said.
Other researchers said the studies were flawed and that a raft of
research has produced evidence linking vaccines to autism. Some
researchers presented data suggesting that some children may not
be able to remove mercury from their bodies normally, which could
allow it to build up and cause brain damage.
The IOM committee is not expected to issue its findings for