Why thimerosal is safe.

Health and medicine explained.
Aug. 2 2005 7:25 AM

Sticking Up for Thimerosal

Read the studies—it's safe.

Hopping on the anti-thimerosal bandwagon 
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Hopping on the anti-thimerosal bandwagon

Bobby Kennedy Jr., a lawyer beloved by the environmental movement for defending rivers and attacking coal-burning power plants, recently discovered a new cause. In a June Rolling Stone article, and in subsequent appearances on Imus in the Morning, ABC News, and The Daily Show With Jon Stewart, he accuses government vaccine scientists and their academic advisers of covering up what for him is an uncontestable fact: the causal link between a mercury-containing preservative called thimerosal in vaccines and a massive increase in childhood autism in America.

As the writer who first told the thimerosal story in depth in the New York Times Magazine two and a half years ago, I have been astonished to see how badly it has been handled since. David Kirby, a Times freelancer, published a supposed exposé in April that tells the story from the perspective of SafeMinds, a group that is to autism what Act Up was to AIDS—sometimes wrong but always loud and overall pretty effective. Then Kennedy entered the fray through his activism against mercury from power plants. In his appearances to champion the thimerosal theory, he trashes establishment science and establishment journalism for having missed the story. But Kennedy's Rolling Stone piece doesn't cover any new ground, and it is full of large and small errors and distortions. Aside from a June 25 New York Times article that discussed the parallel realities of parents and scientists studying thimerosal, there has been little mainstream media response.

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Considering that about 9,000 lawsuits of claims have been filed against thimerosal and have the potential to wreck the pharmaceutical industry, the debate has high stakes. In 1997 Congress ordered the FDA to list all the mercury in food and drug products, and the agency had a "D'oh!" moment in 1999, when it discovered that since 1991 children receiving the normal complement of vaccines had been getting amounts of thimerosal that might push them over EPA-accepted mercury tolerances. To be sure, the EPA recommendations for mercury ingestion were based on studies of methyl mercury, which is generally considered more dangerous than ethyl mercury, the type thimerosal contains. (Read more about the distinction and how it relates to thimerosal's safety.) And the medical literature did not contain a single case of mercury poisoning leading to autism. Still, to be safe, the FDA asked manufacturers to take thimerosal out of vaccines. They did, and most of the thimerosal-containing vaccines were removed from the shelves by early 2002.

Since then, four perfectly good studies comparing large populations of kids have showed that thimerosal did not cause the increased reporting of autism. The best evidence comes from Denmark, which stopped putting thimerosal in vaccines in 1992; the rate of autism in kids born afterward continued to increase. A U.S. studyshowed slightly higher rates of tics in children who got more thimerosal at earlier ages, but no autism. An as yet unpublished study of about 1,000 children exposed to different levels of thimerosal in the United States also showed more tics in the children heavily exposed to thimerosal, but in addition showed they had fewer than average language delays. Both findings were marginally significant in statistical terms—though in unscientific terms, they are probably meaningless.

Parents who are convinced thimerosal damaged their babies attack the big epidemiological studies as a whitewash by vaccine makers. They're especially concerned about the U.S. study, which in its early drafts showed a link between thimerosal and neurodevelopmental problems—though not autism, despite Kennedy's claims to the contrary. He extols the studies by David and Mark Geier, a father-and-son team who work out of their basement in Silver Spring, Md. The Geiers have done a series of studies published in obscure journals that purport toshow a link between autism and mercury, and they spend a lot of their time testifying on behalf of allegedly vaccine-injured kids. In the polite language of the Institute of Medicine report that dismissed the vaccine-autism link, the Geier studies are "uninterpretable." The main Geier approach is to mine data from a CDC reporting system that contains a mishmash of real and garbage vaccine-injury allegations, according to the vast majority of the scientists who work in this area. The Geiers have found a sixfold increase in autism in children who got thimerosal-containing vaccines. But nearly all the reports of autism they tallied came after allegations of the vaccine link had been publicized in the newspapers. In other words, the Geiers report the public's response to a scare as if it were meaningful data.

Probably the most damning epidemiological evidence against the vaccines-cause-autism theory, and another point that Kennedy gets wrong, is contained in the document that got critics started on their claim of a vaccine-provoked epidemic—a 1999 Department of Developmental Services report from California. Like reports from other states in the country, it shows a dramatic increase in autistic children seeking state services, from 2,778 autistics on the rolls in 1987 to 10,360 in 1998. An impressive diagram of this increase was projected on a screen at a Committee for Government Reform hearing chaired by Indiana Republican Dan Burton, who believes that vaccines gave his grandson autism. "Look at that graph," Burton said. "They are having an epidemic out there." But the graph actually vindicated vaccines. MMR vaccination began in children born in 1970, but there was no increase in autism reports in the state until 1980, which also happened to be the first year the psychiatric definition of autism spectrum disorders changed. A 2001 study showed that while MMR vaccination rates increased 14 percent from 1980 to 1994, autism intakes in California's state programs increased 373 percent. The increase also showed no apparent connection to the addition of thimerosal-containing vaccines to state pediatric immunization schedules.

A far more obvious explanation for the increase in autism rates in California was the one that mainstream autism experts expounded: diagnostic changes, new laws that expanded federal payments to care for autistics, and greater parental awareness of these resources. In 1990, Congress made autism one of the disabilities that qualified for federal funding. Thereafter, states were obliged to report all cases of autism. In a Minnesota study, to take one example, admissions of autistic children to developmental programs jumped starting in the 1991 school year and continued to do so for a decade. Often these increases occurred within the same grade. For example, 13 autism cases were reported per 10,000 Minnesota 6-year-olds in the 1995-96 school year—that is, among children born roughly in 1989. Five years later, the prevalence rate for this cohort was reported at 33 per 10,000. These were the same kids. Between the ages of 6 and 11, they'd suddenly "become" nearly three times as autistic—or rather, doctors, parents, and school counselors were enrolling them in programs more aggressively.

Most of the scientists who study autism trends are not ready to rule out entirely some real increase in the disease. But the causes may have nothing to do with industrial toxins like mercury. Interestingly, a 2003 California study found that mothers older than 35 were four times as likely to give birth to autistic children as mothers younger than 20. One of the only known environmental causes of autism is congenital rubella infection (or German measles); during a 1965-66 rubella epidemic in the United States, about 1,500 rubella babies were born with autism in addition to their other handicaps. Other perinatal developments, which increase with maternal age, can't be ruled out.

One of the dynamics that keeps the thimerosal story alive in the autistic community is treatment of the disease with chelators, chemical agents that remove mercury and other heavy metals from the body. The idea is that if chelation improves the behavior of the autistic child, it must be proof that the child was damaged by heavy metals, ergo mercury, ergo the mercury in vaccines. When I speak with parents who believe the thimerosal theory, they talk up recent studies showing that autistic children may have peculiar metabolisms or immune problems that cause them to respond oddly to metals, germs, or even vaccines. Some say their kids have benefited from the chelation therapy. Others don't. Some have children who didn't even get the full load of thimerosal in their vaccines. But they are all angry that establishment medicine is slow to examine the new evidence of biochemical oddities in their children.

I suspect that they are partially right. With new funding for autism research pried loose by SafeMinds' Act Up-style activism, we may soon learn helpful things about the disease and how to treat it. The Institute of Medicine agreed that the special medical problems of some autistics deserve closer scrutiny. But like the Institute of Medicine, I doubt that vaccine damage will figure into the story. And in the meantime, lawsuits could do severe damage to the vaccination programs that protect all of us.

Arthur Allen is the author of The Fantastic Laboratory of Dr. Weigl, Ripe, and Vaccine. He is a health writer and editor at Politico.