As for thimerosal, government precautions
notwithstanding, it was never clear how
threatening it might be. The federal mercury
standards that first heightened concern were
developed for methylmercury, not
ethylmercury, the form contained in
thimerosal. Ethylmercury has less risk of
accumulating to a toxic dose because it does
not last as long in the body. And, according
to the IOM’s 2004 report, there had never
been any evidence of a major incident of
mercury poisoning leading to autism.
The
strongest argument against the idea that
thimerosal poisoned a generation of children
does not emerge from the body of published
studies alone. There is the added detail
that although thimerosal is no longer
present in any recommended childhood
vaccines save the inactivated influenza
vaccine—and hasn’t been, beyond trace
amounts, since 2001—no one is hailing the
end of autism. “If you thought thimerosal
was related to autism, then the incidence of
autism should have gone down,” Harvard’s
McCormick explains. “And it hasn’t.”
In 2005 David Kirby stated that if autism
rates didn’t begin to decline by 2007, “that
would deal a severe blow to the autism-thimerosal
hypothesis.” But as McCormick notes, despite
the absence of thimerosal in vaccines,
reports of autism cases have not fallen. In
a
2008 study published in Archives of
General Psychiatry, two researchers
studying a California Department of
Developmental Services database found that
the prevalence of autism had actually
continued increasing among the young. Kirby
concedes that these findings about the
California database represent a “pretty
serious blow to the thimerosal-causes-autism
hypothesis,” though he does not think they
thoroughly bury it. In an interview, he
outlined many problems with relying on the
California database, suggesting potential
confounding factors such as the state’s high
level of immigration. “Look, I understand
the desire to try to end this and not scare
parents away from vaccination,” Kirby says.
“But I also feel that sometimes that desire
to prove or disprove blinds people on both
sides.”
Kirby says—and even some vaccine
defenders agree—that some small subgroup of
children might have a particular
vulnerability to vaccines and yet be missed
by epidemiological studies. But the two
sides disagree as to the possible size of
that group. “If one or two or three children
every year are getting autism from vaccines,
you would never pick that up,” Offit says.
Kirby, in contrast, feels that while the
idea of thimerosal as the “one and only
cause of autism has gone out the window,” he
still believes there is an “epidemic” with
many environmental triggers and with
thimerosal as a possible contributing
factor.
Meanwhile, in the face of powerful
evidence against two of its strongest
initial hypotheses—concerning MMR and
thimerosal—the vaccine skeptic movement is
morphing before our eyes. Advocates have
begun moving the goalposts, now claiming,
for instance, that the childhood vaccination
schedule hits kids with too many vaccines at
once, overwhelming their immune systems.
Jenny McCarthy wants to “green
our vaccines,” pointing to many other
alleged toxins that they contain. “I think
it’s definitely a response to the science,
which has consistently shown no
correlation,” says David Gorski, a cancer
surgeon funded by the National Institutes of
Health who in his spare time blogs at
Respectful Insolence, a top medical blog
known for its provaccine stance. A hardening
of antivaccine attitudes, mixed with the
despair experienced by families living under
the strain of autism, has heightened the
debate—sometimes leading to blowback against
scientific researchers.
Paul Shattuck did not set out to enrage
vaccine skeptics and the parents of autistic
children. Currently an assistant professor
at the George Warren Brown School of Social
Work at Washington University in St. Louis,
he has dedicated the last decade of his
professional life to helping people with
autism in their families. “Some of my
dearest friends have kids with autism,” he
says.
But in 2006 Shattuck came under fire
after he
published an article in the journal
Pediatrics questioning the existence of
an autism epidemic. No one doubts that since
the early 1990s the number of children
diagnosed with autism has dramatically
increased, a trend reflected in U.S. special
education programs, where children enrolled
as autistic grew from 22,445 in 1994–1995 to
140,254 in 2003–2004. Yet Shattuck’s study
found reasons to doubt that these numbers
were proof of an epidemic. Instead, he
suggested that “diagnostic substitution”—in
which children who previously would have
been classified as mentally retarded or
learning disabled were now being classified
on the autism spectrum—played a significant
role in the apparent increase.
Shattuck did not reject the idea that
rising autism levels might be in part due to
environmental causes; he merely showed the
increase was largely an artifact of changing
diagnostic practices, which themselves had
been enabled by rising levels of attention
to autism and its listing as a diagnostic
category in special education. Yet simply by
questioning autism epidemic claims in a
prominent journal, he became a target.
“People were obviously Googling me and
tracking me down,” he recalls. Shattuck
emphasizes that most e-mails and calls
merely delivered “heartfelt pleas from
people with very sick kids who’ve been led
to believe a particular theory of etiology.”
The bulk weren’t menacing, but a few
certainly were.
Others attacked Shattuck’s research on
the Web and insinuated that he had
fabricated his data or committed scientific
misconduct. “It was dismaying to feel like
people were calling me a traitor to autistic
kids and families,” he says.
“If there has been a more harmful urban
legend circulating in our society than the
vaccine-autism link,” University of
Pennsylvania bioethicist
Arthur Caplan wrote in The
Philadelphia Inquirer, “it’s hard to
know what it might be.” One type of harm, as
Shattuck’s story shows, is to individual
scientists and the scientific process. There
is a real risk that necessary research is
being held back as scientists fear working
in such a contested field. Shattuck’s
experience is not unique. Offit cannot go on
a book tour to promote Autism’s False
Prophets because of the risk involved
in making public appearances. He has
received too many threats.
Yet another cost comes in the rush toward
unproven, and potentially dangerous,
alternative therapies to treat autism. It is
easy to sympathize with parents of autistic
children who desperately want to find a
cure, but this has led to various
pseudoremedies whose efficacy and safety
have been challenged by science. These
include facilitated communication, secretin
infusion, chelation therapy (which involves
pumping chemicals into the blood to bind
with heavy metals such as mercury), and
hormonal suppression. It is estimated that
more than half of all children with autism
are now using “complementary and
alternative” treatments.
Disease, however, is the greatest danger
associated with holding back vaccines amid
the ongoing investigation of dubious claims.
Both the vaccinated and the unvaccinated
populations are placed at greater risk.
Given enough vaccine exemptions and
localized outbreaks, it is possible that
largely vanquished diseases could become
endemic again. (That is precisely what
happened with
measles in 2008 in the U.K., following
the retreat from the MMR vaccine in the wake
of the 1998 scare.) The public-health costs
of such a development would be enormous—and
they would not impact everyone equally. “If
vaccine rates start to drop, who’s going to
get affected?” Peter Hotez asks. “It’s going
to be people who live in poor, crowded
conditions. So it’s going to affect the
poorest people in our country.”
Paradoxically, the great success of
vaccines is a crucial reason why
antivaccination sentiment has thrived, some
scientists say. Most of the diseases that
vaccines protect against have largely been
licked. As a consequence, few people
personally remember the devastation they can
cause. So with less apparently on the line,
it is easier to indulge in the seeming
luxury of vaccine skepticism and avoidance.
Even before the recent spike in attention to
thimerosal, members of the public were
alarmingly skeptical of vaccines. In a 1999
survey, 25 percent felt their children’s
immune systems could be harmed by too many
vaccinations, and 23 percent shared the
sentiment that children receive more
vaccinations than are healthy. There is
every reason to think that those
numbers—gathered before the vaccine-autism
controversy reached anything like its
current intensity—have risen since.