Research has soundly disproved the alleged connection, yet fears about vaccines continue to be a major risk to public health.by Chris Mooney
Vaccines do not cause autism. That was the ruling in each of three critical test cases handed down on February 12 by the U.S. Court of Federal Claims in Washington, D.C. After a decade of speculation, argument, and analysis—often filled with vitriol on both sides—the court specifically denied any link  between the combination of the MMR vaccine and vaccines with thimerosal (a mercury-based preservative) and the spectrum of disorders associated with autism. But these rulings, though seemingly definitive, have done little to quell the angry debate, which has severe implications for American public health.
The idea that there is something wrong with our vaccines—that they have poisoned a generation of kids, driving an “epidemic” of autism—continues to be everywhere: on cable news, in celebrity magazines, on blogs, and in health news stories. It has had a particularly strong life on the Internet, including the heavily trafficked Huffington Post , and in pop culture, where it is supported by actors including Charlie Sheen and Jim Carrey, former Playboy playmate Jenny McCarthy, and numerous others. Despite repeated rejection by the scientific community, it has spawned a movement, led to thousands of legal claims, and even triggered occasional harassment and threats against scientists whose research appears to discredit it.
You can see where the emotion and sentiment come from. Autism can be a terrible condition, devastating to families. It can leave parents not only aggrieved but desperate to find any cure, any salvation. Medical services and behavioral therapy for severely autistic children can cost more than $100,000 a year, and these children often exhibit extremely difficult behavior. Moreover, the incidence of autism is apparently rising rapidly. Today one in every 150  children has been diagnosed on the autism spectrum; 20 years ago that statistic was one in 10,000. “Put yourself in the shoes of these parents,” says journalist David Kirby, whose best-selling 2005 book, Evidence of Harm, dramatized the vaccine-autism movement. “They have perfectly normal kids who are walking and happy and everything—and then they regress.” The irony is that vaccine skepticism—not the vaccines themselves—is now looking like the true public-health threat.
The decadelong vaccine-autism saga began in 1998, when British gastroenterologist Andrew Wakefield and his colleagues published evidence  in The Lancet suggesting they had tracked down a shocking cause of autism. Examining the digestive tracts of 12 children with behavioral disorders, nine of them autistic, the researchers found intestinal inflammation, which they pinned on the MMR (measles, mumps, and rubella) vaccine. Wakefield had a specific theory of how the MMR shot could trigger autism: The upset intestines, he conjectured, let toxins loose in the bloodstream, which then traveled to the brain. The vaccine was, in this view, effectively a poison. In a dramatic press conference, Wakefield announced the findings and sparked an instant media frenzy. For the British public, a retreat from the use of the MMR vaccine—and a rise in the incidence of measles—began.
In the United States, meanwhile, fears would soon arise concerning another means by which vaccines might induce autism. Many vaccines at the time contained thimerosal, a preservative introduced in the 1930s to make vaccines safer by preventing bacterial contamination. But thimerosal is 50 percent mercury by weight, and mercury is known to be a potent neurotoxin, at least in large doses. In 1999 new federal safety guidelines for mercury in fish stirred concerns about vaccines as well.
The U.S. government responded by ordering that thimerosal be removed from all vaccines administered to children under age 6, or reduced to trace amounts. (Some inactivated influenza vaccines were exempted.) The step was described as a “precautionary” measure. There was no proof of harm, government researchers said, just reason to worry that there might be. Meanwhile, scientists launched numerous studies to determine whether thimerosal had actually caused an autism epidemic, while some parents and their lawyers started pointing fingers and developing legal cases.
Within weeks of this year’s federal court decisions—which examined and vindicated both the MMR vaccine and thimerosal—environmental lawyer Robert F. Kennedy Jr. wrote a column  in The Huffington Post in which he continued to press his case that the government has peddled unsafe vaccines to an unsuspecting public. It is a cause he has championed since 2005, when he published “Deadly Immunity” in Rolling Stone  and Salon  magazines. The article was a no-holds-barred denunciation of the U.S. public-health establishment, purporting to tell the story of how “government health agencies colluded with Big Pharma to hide the risks of thimerosal from the public…a chilling case study of institutional arrogance, power, and greed.” Half a decade after the original thimerosal concerns were first raised, Kennedy claimed to have found the smoking gun: the transcript of a “secret” 2000 meeting of government, pharmaceutical, and independent researchers with expertise in vaccines. Kennedy’s conclusion: The generational catastrophe was real; our kids had been poisoned. If true, it would be perhaps the greatest biomedical catastrophe in modern history.
“It’s not hard to scare people,” says pediatrician and leading vaccine advocate Paul Offit. “But it’s extremely difficult to unscare them.”
But for Kennedy to be right, a growing consensus in the medical establishment had to be wrong. Indeed, Kennedy blasted a leading organ of science that had just vindicated both the MMR vaccine and thimerosal, the Institute of Medicine (IOM). “The CDC paid the Institute of Medicine to conduct a new study to whitewash the risks of thimerosal,” Kennedy wrote, “ordering researchers to ‘rule out’ the chemical’s link to autism.” In reality, the IOM—a branch of the National Academy of Sciences (NAS), the government’s top independent scientific adviser—carefully creates firewalls between the funding it receives to conduct scientific assessments and the results it ultimately produces. “Funders don’t control the composition of the committee, and they don’t meet with the committee,” says Harvard public-health researcher Marie McCormick, who chaired the IOM vaccine-safety committee in question. “And on no NAS or IOM committee are the members paid; they all work pro bono. There’s no reason for them not to look at the data.”
The same year Kennedy’s article came out, journalist David Kirby published Evidence of Harm—Mercury in Vaccines and the Autism Epidemic: A Medical Controversy. He followed a group of parents from the Coalition for SafeMinds, an autism activist organization. They had grown convinced that vaccines and other environmental factors had caused their children’s conditions. Kirby’s chronicle of the parents’ efforts to publicize the dangers of vaccines became a best seller and greatly advanced SafeMinds’ cause.
Yet even as vaccine hysteria reached a fever pitch in the wake of Kennedy’s and Kirby’s writings, the scientific evidence was leaning strongly in the other direction. In discounting the dangers of both the MMR vaccine and thimerosal, the IOM had multiple large epidemiological studies to rely on. For MMR, the IOM examined  16 studies. All but two, which were dismissed because of “serious methodological flaws,” showed no evidence of a link. For thimerosal, the IOM looked at  five studies, examining populations in Sweden, Denmark, the United Kingdom, and the United States (studies that vaccine critics contend were flawed). Since then, further research has strengthened and vindicated the committee’s original conclusion. It is a conclusion that has been “independently reached by scientific and professional committees around the world,” as a recent science journal commentary noted. Either the scientific community has found a clear, reassuring answer to the questions raised about thimerosal in vaccines, or there is a global scientific conspiracy to bury the truth.
Whether the public is hearing the scientific community’s answer is another matter. “It’s not hard to scare people,” says pediatrician and leading vaccine advocate Paul Offit, who himself coinvented a vaccine. “But it’s extremely difficult to unscare them.”
A backlash against vaccine skeptics is beginning to mount. Standing up to fellow celebrities, actress Amanda Peet, who recently vaccinated her baby daughter, has become a spokeswoman for the pro-vaccine group Every Child by Two . Offit’s book Autism’s False Prophets has further galvanized vaccine defenders—not only by debunking the science of those who claim vaccines are dangerous but also by contending that the parents of autistic children and the children themselves are indeed victims, not of vaccines but of medical misinformation.
The provaccine case starts with some undeniable facts: Vaccines are, as the IOM puts it, “one of the greatest achievements of public health.” The CDC estimates that thanks to vaccines, we have reduced morbidity by 99 percent or more for smallpox, diphtheria, measles, polio, and rubella. Averaged over the course of the 20th century, these five diseases killed nearly 650,000 people annually. They now kill fewer than 100. That is not to say vaccines are perfectly safe; in rare cases they can cause serious, well-known adverse side effects. But what researchers consider unequivocally unsafe is to avoid them. As scientists at the Johns Hopkins Bloomberg School of Public Health recently found while investigating whooping cough  outbreaks in and around Michigan, “geographic pockets of vaccine exemptors pose a risk to the whole community.”
When it comes to autism, vaccine defenders make two central claims. First, the condition is likely to be mostly genetic rather than environmentally caused; and second, there are reasons to doubt whether there is really a rising autism epidemic at all.
It is misleading to think of autism as a single disorder. Rather, it is a spectrum of disorders showing great variability in symptoms and expression but fundamentally characterized by failed social development, inability to communicate, and obsessive repetitive behavior. Autism generally appears in children at early ages, sometimes suddenly, and its genetic component has long been recognized. Studies have shown that if one identical twin has autism, there is at least a 60 percent chance that the other also does. “From my point of view, it’s a condition associated with genetic defects and developmental biology problems,” says Peter Hotez, a George Washington University microbiologist and father of an autistic child. Hotez, who is also president of the Sabin Vaccine Institute, says, “I don’t think it’s possible to explain on the basis of any vaccine toxin that is acquired after the baby is born.” Still, scientists cannot fully rule out environmental triggers—including various types of toxicity—that might interact with a given individual’s preexisting genetic inclination. Autism is a complex disorder with multiple forms of expression and potentially multiple types of causation that are incompletely understood.
As for whether autism is rising, a number of experts say it is hard to know. Is the increase real, or is it largely the result of more attention to the condition, an expansion of the autism spectrum to embrace many different heterogeneous disorders, a new focus on children classified as autistic in federal special education programs during the 1990s, and other factors? It could be some combination of all these things.
But if environmental triggers of autism cannot be ruled out, the idea that those triggers can be found in the MMR vaccine or in thimerosal has crumbled under the weight of scientific refutation. Epidemiological studies have cast grave doubt on Andrew Wakefield’s MMR hypothesis—and so have subsequent scandals. Nearly all of Wakefield’s coauthors have since retracted the autism implications  of their work; The Lancet has also backed away from the study. A series of investigative stories published in The Times of London unearthed Wakefield’s undisclosed ties to vaccine litigation in the U.K. and, more recently, suggested he fabricated  his data (which Wakefield denies).
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. Ethyl