Denialism: How Irrational Thinking Hinders Scientific Progress, Harms the Planet, and Threatens Our Lives - Michael Specter (2009)

Chapter 2. Vaccines and the Great Denial

Marie McCormick is a studious and reserved woman with the type of entirely unthreatening demeanor that comes in handy in her job as a professor of pediatrics at the Harvard School of Public Health. She has devoted most of the past four decades to preparing physicians to nurture mothers and their children, and, since her days as a student at Johns Hopkins, has focused much of her research on high-risk newborns and infant mortality. Like many prominent academic physicians, her renown had largely been restricted to her field. Until 2001.

That was the year she was asked to lead a National Academy of Sciences commission on vaccine safety. The Immunization Safety Review Committee was established by the Institute of Medicine to issue impartial, authoritative, and scientifically rigorous reports on the safety of vaccinations. Its goal, while vital, seemed simple enough: bring clarity to an issue where too often confusion reigned. McCormick took on the assignment readily, although she was surprised at having been selected. It was not as if she considered vaccine safety unimportant—the issue had preoccupied her for decades. Nonetheless, vaccines were not McCormick’s area of expertise and she couldn’t help thinking that there must be someone better suited to the job. “My research has always been on the very premature,” she explained. “So I was a bit naive about why they might want me to run that committee.” She soon made a discovery that surprised her: “I realized that all of us on the committee were selected because we had no prior contact with vaccines, vaccine research, or vaccine policy. We all had very strong public health backgrounds, but we were just not clear about the nature or intensity of the controversy.”

The controversy that the panel set out to address was whether the benefits of receiving childhood vaccines outweighed the risks. In particular, the committee was asked to investigate the suggested link between the measles, mumps, and rubella inoculation routinely administered between the ages of one and two and the development of autism, which often becomes apparent at about the same time. The incidence of autism has risen dramatically during the past three decades, from less than one child in twenty-five hundred in 1970 to nearly one in every 150 today. That amounts to fifty new diagnoses of autism or a related disorder every day—almost always in children who seem to be developing normally, until suddenly their fundamental cognitive and communication skills begin to slip away.

Parents, understandably desperate to find a cause and often wholly unfamiliar with many diseases that vaccines prevent, began to wonder—publicly and vocally—why their children even needed them. There could be no better proof of just how effective those vaccines have been. With the sole exceptions of improved sanitation and clean drinking water, no public health measure has enhanced the lives of a greater number of people than the widespread adoption of vaccinations, not even the use of antibiotics. Cholera and yellow fever, both ruthless killers, are hardly known now in the developed world. Until vaccines were discovered to stop them, diphtheria and polio rolled viciously through America every year, killing thousands of children, paralyzing many more, and leaving behind ruined families and a legacy of terror. Both are gone. So is mumps, which in the 1960s infected a million children every year (typically causing them to look briefly like chipmunks, but occasionally infiltrating the linings of the brain and spinal cord, causing seizures, meningitis, and death).

Even measles, an illness that most young parents have never encountered, infected nearly four million Americans annually until 1963, when a vaccine was introduced. Typically, hundreds died, and thousands would become disabled for life by a condition called measles encephalitis. (In parts of the developing world, where vaccines are often unavailable, measles remains an unbridled killer: in 2007, about two hundred thousand children died from the disease—more than twenty every hour.) In the United States, fifty-two million measles infections were prevented in the two decades after the vaccine was released. Without the vaccine, seventeen thousand people would have been left mentally retarded, and five thousand would have died. The economic impact has also been dramatic: each dollar spent on the MMR vaccine saves nearly twenty in direct medical costs. That’s just money; in human terms, the value of avoiding the disease altogether cannot be calculated. By 1979, vaccination had even banished smallpox, the world’s most lethal virus, which over centuries had wiped out billions of people, reshaping the demographic composition of the globe more profoundly than any war or revolution.

Those vaccines, and others, have prevented unimaginable misery. But the misery is only unimaginable to Americans today because they no longer need to know such diseases exist. That permits people to focus on risks they do confront, like those associated with vaccination itself. Those risks are minute, and side effects are almost always minor—swelling, for instance; a fever or rash. Still, no medical treatment is certain to work every time. And serious adverse reactions do occur. If you hunt around the Internet for an hour (or ten) you might think that nobody pays attention to vaccine safety in America today. The Public Health Service has actually never been more vigilant. For example, in 1999 the Centers for Disease Control called for an end to the use of the oral polio vaccine, developed by Albert Sabin, which, because it contained weakened but live virus, triggered the disease in about ten people out of the millions who took it each year. (A newer injectable and inactivated version eliminates even this tiny threat.) Despite legitimate concerns about safety, every vaccine sold in the United States is scrutinized by at least one panel of outside advisers to the Food and Drug Administration before it can be licensed; many don’t even make it that far. As a result, vaccination for virtually every highly contagious disease is never as dangerous as contracting the infections those vaccines prevent.

Prevention is invisible, though, and people fear what they cannot see. Nobody celebrates when they avoid an illness they never expected to get. Humans don’t think that way. Choosing to vaccinate an infant requires faith—in pharmaceutical companies, in public health officials, in doctors, and, above all, in science. These days, that kind of faith is hard to come by. So despite their success, there has been no more volatile subject in American medicine for the past decade than the safety of vaccines. There is a phrase used commonly in medicine: “true, true, and unrelated.” It is meant to remind physicians not to confuse coincidence with cause. That kind of skepticism, while a fundamental tenet of scientific research, is less easily understood by laymen.

For most people, an anecdote drawn from their own lives will always carry more meaning than any statistic they might find buried in a government report. “Neither my husband nor anyone in his family has ever been vaccinated … and there isn’t a single person in his family who has ever had anything worse than a cold,” one woman wrote on the heavily read blog Mom Logic. “Myself and my family, on the other hand, were all vaccinated against every possible thing you could imagine… . Somehow we all got the flu every single year. Somehow everyone in my family is chronically ill. And amazingly, when the people in my family reach 50 they are all old and deteriorated. In my husband’s family they are all vibrant into their late 90’s. My children will not be vaccinated.”

This particular epidemic of doubt began in Britain, when the Lancet published a 1998 study led by Dr. Andrew Wakefield in which he connected the symptoms of autism directly to the MMR vaccine. The study was severely flawed, has been thoroughly discredited, and eventually ten of its thirteen authors retracted their contributions. Yet the panic that swept through Britain was breath-taking: vaccination rates fell from 92 percent to 73 percent and in parts of London to nearly 50 percent. Prime Minister Tony Blair refused repeatedly to respond to questions about whether his youngest child, Leo, born the year after Wakefield’s study, received the standard MMR vaccination. Blair said at the time that medical treatment was a personal matter and that inquiries about his children were unfair and intrusive. No virus respects privacy, however, so public health is never solely personal, as the impact on Britain has shown. England and Wales had more cases of measles in 2006 and 2007 than in the previous ten years combined. In 2008, the caseload grew again—this time by nearly 50 percent. The numbers in the United States have risen steadily as well, and the World Health Organization has concluded that Europe, which had been on track to eliminate measles by 2010, is no longer likely to succeed. Vaccination rates just aren’t high enough.

Fear is more infectious than any virus, and it has permitted politics, not science, to turn one of the signature achievements of modern medicine into fodder for talk show debates and marches on Washington. Celebrities like Jenny McCarthy, who oppose the need for a standard vaccination schedule, denounce celebrities like Amanda Peet who are willing to say publicly that the benefits of vaccines greatly outweigh the risks. Peet represents Every Child by Two, a nonprofit organization that supports universal vaccination. Not long after she began speaking for the group, Peet and McCarthy began to clash. At one point, McCarthy reminded Peet that she was right because “there is an angry mob on my side.” When three physicians, appearing on Larry King Live, disagreed with McCarthy, she simply shouted “Bullshit!” in response. When that didn’t shut them up, she shouted louder. Data, no matter how solid or frequently replicated, seems beside the point.

What does it say about the relative roles that denialism and reason play in a society when a man like Blair, one of the democratic world’s best-known and most enlightened leaders, refused at first to speak in favor of the MMR vaccine, or when a complete lack of expertise can be considered a requirement for participation in America’s most prominent vaccine advisory commission? “Politically, there is simply no other way to do it,” Anthony S. Fauci explained. “Experts are often considered tainted. It is an extremely frustrating fact of modern scientific life.” Fauci has for many years run the National Institute of Allergy and Infectious Diseases, where at the beginning of the AIDS epidemic he emerged as one of the public health establishment’s most eloquent and reliably honest voices. He shook his head in resignation when asked about the need for such a qualification, but noted that it has become difficult to place specialists on committees where politics and science might clash. “You bring people with histories to the table and they are going to get pummeled,” he said. “It would simply be war.”

War is exactly what the vaccine commission got. During McCormick’s tenure, the National Academy of Sciences published several reports of its findings. In a 2001 study, Measles-Mumps-Rubella Vaccine and Autism, the committee concluded that there was no known data connecting MMR immunizations with the spectrum of conditions that are usually defined as autism. The wording left room for doubt, however, and the report resolved nothing. Three years later, with vaccination rates falling in the United States and anxiety among parents increasing rapidly, and after many calls from physicians for clearer and more compelling guidance, the committee revisited the issue more directly.

Even at the height of the age of AIDS, when members of the activist group ACT UP stormed St. Patrick’s Cathedral, surrounded the White House, shut down the New York Stock Exchange, and handcuffed themselves to the Golden Gate Bridge, all to protest the prohibitive cost of drug treatments and the seemingly endless time it took to test them, rancor between researchers and the advocacy community was rare. The contempt AIDS activists felt for federal officials—particularly for the Food and Drug Administration and its cumbersome regulations—was palpable. Even the most strident among them however, seemed to regard physicians as allies, not enemies.

Those days have ended, as the Institute of Medicine vaccine committee came to learn. For years, the culprits most frequently cited as the cause of autism had been the measles, mumps, and rubella vaccine, as well as those that contained the preservative thimerosal. Thimerosal was first added to vaccines in the 1930s in order to make them safer. (Before that, vaccines were far more likely to cause bacterial infections.) While descriptions of autistic behavior have existed for centuries, the disease was only named in 1943—and its definition continues to evolve. Neurodevelopmen tal illnesses like autism have symptoms similar to those of mercury poisoning, and there is mercury in thimerosal. What’s more, American children often receive a series of vaccinations when they are about eighteen months old. That is a critical threshold in human development, when a child often begins to form simple sentences and graduates from chewing or pawing toys to more engaging and interactive forms of play. Some children don’t make that transition—and because they receive so many shots at the same time, many parents feared, naturally enough, that the inoculations must have been the cause.

Anguished parents, who had watched helplessly and in horror as their children descended into the disease’s unending darkness, could hardly be faulted for making that connection and demanding an accounting. The Immunization Safety Review Committee was supposed to provide it, although its members represented an establishment trusted by few of those who cared most passionately about the issue. AIDS activism had its impact here too, because it changed American medicine for good: twenty-first-century patients no longer act as if their doctors are deities. People demand to know about the treatments they will receive, and patient groups often possess more knowledge than the government officials entrusted to make decisions about their lives. They have every right to insist on a role in treating the diseases that affect them.

The rise of such skepticism toward the scientific establishment (as well as the growing sense of anxiety about environmental threats to our physical health) has led millions to question the authority they once granted, by default, not only to their doctors, but also to organizations like the National Academy of Sciences. Faced with the medical world that introduced, approved, and relentlessly promoted Vioxx, a patient can hardly be blamed for wondering, “What do these people know that they are not telling me?” Uncertainty has always been a basic ingredient of scientific progress—at least until reason is eclipsed by fear. Unlike other commodities, the more accessible knowledge becomes, the more it increases in value. Many autism activists, however, sensed that federal health officials and researchers who work with them were guilty of avarice and conspiracy, or at least of laziness—guilty until proven innocent (and innocence is hard to prove). To use Fauci’s formulation, when experts are tainted, where can you place your trust?

It was, in the highly emotional words of one vaccine activist who rejects the federal government’s approach, a conspiracy among scientists to protect pharmaceutical companies at the expense of America’s children. Because this is the age of denialism, evidence that any pharmaceutical company has engaged in venal behavior means that they all have. “When mothers and fathers take their healthy sons and daughters to pediatricians to get vaccinated and then witness them suffering vaccine reactions and regressing into chronic poor health within hours, days and weeks of getting sometimes five to ten vaccines on one day, they are not going to accept an illogical, unscientific explanation like ‘it’s all a coincidence,’ ” Barbara Loe Fisher has written. Fisher is the leader of the National Vaccine Information Center, the most influential of the many groups that oppose universal vaccination. (This sentiment, that children receive too many vaccinations when they are young, also draws frequently on anecdotal experience and the sort of conspiracy theories that are hallmarks of denialism: “No wonder our children are damaged and dealing w/ADHD, autism, diabetes, asthma, allergies, etc.,” Fisher wrote. “Forty-eight doses of fourteen vaccines by age 6 is excessive and is only for the benefit of the drug companies who promote fear to fund their bottom line.”)

The vaccine panel found itself at ground zero in this war against authority and scientific rigor. “It was the perfect storm,” McCormick told me one day when we met in her office at Harvard. “Because all of a sudden we had the expansion of shots, the issue of the mercury in vaccines, and this rapid rise in the diagnosis of autism. Everyone put two and two together and came out with six.” In a society where numeracy is rarely prized and subjective decisions often outweigh rational choices, it’s not hard to understand at least some of the reasons why that happened: science works slowly and has yet to determine a cause for autism, which isn’t even a single “disease,” but rather a complex set of developmental disorders. In fact, it makes no more sense to talk about “curing” autism than it does to discuss a cure for cancer; “cancer” is an umbrella term for many diseases characterized by malignant growth. A successful treatment for leukemia won’t stop the spread of melanoma. Effective treatments for autism will require a fuller understanding of how those developmental disorders differ—but they can differ widely. Autism spectrum disorders vary in severity from mild conditions like Asperger’s syndrome to those characterized by sustained impairments in social interaction and communication abilities.

When “experts,” often with degrees or licenses that seem impressive, suddenly emerge to tell heartbroken family members that there is a simple solution to their problems, who wouldn’t want to believe it might be true? And with the help of the Internet, those experts are just a mouse click away. People often cling to their initial response when they discover something profoundly disturbing, even if more compelling evidence emerges. It’s a form of denialism, but also a common human instinct. Not surprisingly, then, the vaccine panel was indeed “pummeled” during its deliberations. Attacks came by e-mail and over the telephone. One member was effectively forced to resign after he received an escalating series of personal (and credible) threats that eventually became so worrisome that McCormick agreed to shift the venue of the committee’s final public meeting to a room where the members would be able to come and go in safety, interacting with the audience behind a human moat of security guards. Like a jury deciding the fate of a gangland leader, committee members were encouraged to stay in a single hotel, discuss the location with no one, and refrain from wandering about town on their own. Security was tightened; all this before the committee made its final report. When it came time for the meeting, each member was loaded onto a bus and driven directly to a garage beneath the main building of the National Academy of Sciences. That way, they could make it to the hearing room without having to run the gauntlet of protestors.

THE REPORT, Vaccines and Autism, was issued in May 2004. After an exhaustive analysis of the available data, and after review by another independent panel, the committee concluded that there was no evidence to suggest the existence of any relationship between the two. “There really wasn’t any doubt about the conclusions,” McCormick said. “The data were clear.” The Institute of Medicine team attempted to review every important epidemiological study, whether published or not, involving hundreds of thousands of children in several countries. They set out with a clear goal: to discover what biological mechanisms involved in immunizations might cause autism. Yet, no matter where they looked or how they parsed the data, the central results never varied: unvaccinated children developed autism at the same or higher rate as those who had been vaccinated. The panel reported accordingly: “The committee concludes that the body of epidemiological evidence favors rejection of a causal relationship between the MMR vaccine and autism.”

The report also pointed out that the mercury contained within the preservative thimerosal, which had been used widely in vaccines for nearly seventy years, caused no apparent harm. Thimerosal had been a focus of special fury among anti-vaccine activists. By July 1999, however, two years before the IOM committee was convened, the preservative had been ordered removed from childhood vaccines as a precautionary measure. Vaccine manufacturers, under fierce public pressure, had agreed with the Centers for Disease Control and the American Academy of Pediatrics. “Parents should not worry about the safety of vaccines,” the academy said at the time. “The current levels of thimerosal will not hurt children, but reducing those levels will make safe vaccines even safer. While our current immunization strategies are safe, we have an opportunity to increase the margin of safety.” In other words, they decided it would be easier to get rid of the controversy than to explain it.

The decision, an attempt to placate parents, had no basis in scientific research, and set off a cascading wave of misunderstanding that persists to this day. Almost immediately, advocacy groups arose, filled with members who were convinced thimerosal had caused their children’s autism. “It was a decision that was made very abruptly,” McCormick, who had no role in making it, told me. “And with not very good communication between professionals and the public. Maybe they should have thought about what you might want to know to reassure people and that is a valid concern of parents. You know how this looks: ‘Last year you told me this was safer than blazes, and this year you are taking it out of the drinking water. Hmm … how can I possibly trust a word you say?’ ” At the time, little was known about the toxicity of ethyl mercury, the chemical compound in thimerosal—so almost all toxicology data about mercury in vaccines was inferred from research into a related molecule, methyl mercury, which is found in fish that we eat and is used heavily in industry. While everyone has tiny amounts of methyl mercury in their bodies, the less the better, particularly because it can take months to be eliminated from our tissues.

The IOM examined the hypothesis that vaccinated children would develop a particular type of autism, caused by mercury poisoning. Presumably those children would develop symptoms at a different age than those who were not vaccinated. Yet in an analysis of tens of thousands of children, no statistical age difference was discovered. Furthermore, if, as so many parents and advocacy groups still believe, there is a link between thimerosal and autism, one would assume that the number of children diagnosed with the illness would have decreased rapidly after the middle of 2000, by which time the preservative had been removed from nearly every childhood vaccine. Researchers in Montreal had a unique opportunity to test this hypothesis because in the 1980s Canada began to phase out thimerosal slowly over a decade. As a result, Canadian infants born in the years between 1987 and 1998 could have received nearly any amount of thimerosal in vaccines, from none to 200 micrograms, the latter being nearly the maximum daily dose that had been permitted in the United States. The Canadian team was able to study discrete groups and found that autism was most prevalent among children who received vaccines that contained no mercury.

Epidemiologists in Finland pored over the medical records of more than two million children, also finding no evidence that the vaccine caused autism. In addition, several countries removed thimerosal from vaccines before the United States. Studies in virtually all of them—Denmark, Canada, Sweden, and the United Kingdom—found that the number of children diagnosed with autism continued to rise throughout the 1990s, after thimerosal had been removed. All told, ten separate studies failed to find a link between MMR and autism; six other groups failed to find a link between thimerosal and autism. It is impossible to prove a negative—that a relationship between thimerosal and autism does not exist. While data can’t prove that, it has failed to find any connection between them in any significant study. Because of the strength, consistency, and reproducibility of the research, the notion that MMR or thimerosal causes autism no longer seemed to public health officials like a scientific controversy.

The panel attempted to be definitive: “The committee also concludes that the body of epidemiological evidence favors rejection of a causal relationship between thimerosal-containing vaccines and autism. The committee further finds that potential biological mechanisms for vaccine-induced autism that have been generated to date are theoretical only. The committee does not recommend a policy review of the current schedule and recommendations for the administration of either the MMR vaccine or thimerosal-containing vaccines.” The report suggested that people forget about thimerosal (which by then remained only in certain flu vaccines) and the controversy behind it. After all the research, thimerosal may be the only substance we might say with some certainty doesn’t cause autism; many public health officials have argued that it would make better sense to spend the energy and money searching for a more likely cause.

It didn’t take long for the findings, and the finality with which they were delivered, to generate reactions. Boyd Haley, professor of chemistry at the University of Kentucky and a witness who has often testified about his beliefs that mercury in thimerosal caused autism, was “amazed and astounded” that the IOM would conclude otherwise. Haley is also a prominent “amalgam protestor,” convinced that trace amounts of mercury in dental fillings cause Alzheimer’s disease, although no data exists to support that view. “The dismissal of thimerosal as causal to autism is outrageous!” he said. “It reflects a level of ignorance that is unacceptable for a scientific review committee. This is disgraceful and puts into question the very credibility of every oversight government authority in the United States. Exposure to thimerosal (mercury) causes a biochemical train wreck. I’m flabbergasted.”

His was far from a lonely voice of outrage. The day the 2004 report was released, Indiana representative Dan Burton erupted. “This research does a disservice to the American people,” he stated. Burton had long been a vociferous critic of the public health establishment and was well known for doubting many of the tenets of conventional medicine. “My only grandson became autistic right before my eyes—shortly after receiving his federally recommended and state-mandated vaccines,” he said in 2002. In an October 25, 2000, letter to the Department of Health and Human Services, acting in his role as chairman of the House Committee on Government Reform, Burton asked the agency’s director to force the Food and Drug Administration to recall all vaccines containing thimerosal. “We all know and accept that mercury is a neurotoxin, and yet the FDA has failed to recall the 50 vaccines that contain Thimerosal,” Burton wrote, adding, “Every day that mercury-containing vaccines remain on the market is another day HHS is putting 8,000 children at risk.” (The letter was sent more than a year after voluntary withdrawal turned exposure to thimerosal, which remained in only some flu vaccines, into a rarity.)

It would be easy enough, and to many people comforting, to dismiss Burton as a fringe figure—his active indifference to scientific achievement and his opinions on health matters are highly publicized and widely considered ludicrous. If he is a fringe figure, however, he has unique power and many followers. The controversy not only continued, but intensified. Politicians have not shied away from using thimerosal as a public relations tool. On September 28, 2004, Arnold Schwarzenegger, governor of California, banned thimerosal-containing vaccines from his state for children and pregnant women. Other states soon did so as well.

No prominent American has spoken with more conviction about the putative dangers of vaccines or their relationship to autism than Robert F. Kennedy Jr. To him, the IOM report proved only that “the CDC paid the Institute of Medicine to conduct a new study to whitewash the risks of thimerosal,” he wrote in 2005, “ordering researchers to ‘rule out’ the chemical’s link to autism.” That year, Kennedy, whose environmental work for the Hudson Riverkeeper organization has often been praised, published an article in Rolling Stone (and on the Internet at Salon.com) called “Deadly Immunity.” It was, he wrote, “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… . I was drawn into the controversy only reluctantly. As an attorney and environmentalist who has spent years working on issues of mercury toxicity, I frequently met mothers of autistic children who were absolutely convinced that their kids had been injured by vaccines.” He went on to say that he was skeptical until he read the scientific studies and looked at the data.

“Deadly Immunity” was a landmark in the history of science journalism, combining Kennedy’s celebrity star power with a stinging assault on reason and scientific fact. The piece was riddled with inaccuracies, filled with presumptions for which there was no supporting data, and knit together by an almost unimaginable series of misconceptions. Kennedy largely framed his piece around quotes taken from the transcripts of a scientific meeting where members of the Immunization Safety Review Committee had gathered to plan their work. Those quotes appeared particularly to damn Dr. McCormick, the committee leader. According to Kennedy’s article, McCormick told her fellow researchers when they first met in January 2001 that the CDC “wants us to declare, well, that these things are pretty safe,” and “we are not ever going to come down that [autism] is a true side effect” of thimerosal exposure. In other words, before the committee even began its work, Kennedy asserts, McCormick had closed her mind to the possibility of a connection between thimerosal and autism. It was exactly the kind of conspiracy people concerned about the effects of the MMR vaccine had feared.

The transcripts tell a starkly different story. It’s never hard to build a case with a partial quote; denialists do it every day, relying on fragmentary evidence and facts taken out of context. Here is what McCormick said: “I took away [from the previous day’s discussion] actually an issue that we may have to confront, and that is actually the definition of what we mean by safety. It is safety on a population basis, but it is also safety for the individual child. I am wondering, if we take this dual perspective, we may address more of the parent concerns, perhaps developing a better message if we think about what comes down the stream as opposed to CDC, which wants us to declare, well, these things are pretty safe on a population basis.”

As Harvey Feinberg, the former dean of the Harvard School of Public Health who is now head of the Institute of Medicine, pointed out at the time, the full quote was part of a discussion that focused on two issues: the need for parents to learn whether a vaccine was safe for an individual child who might be sick, and the public health community’s right to know if vaccines pose risks to a larger population. In fact, McCormick proposed that the committee consider addressing the parental concerns about the health of an individual child—in addition to the CDC’s concern about population-wide effects. McCormick’s approach, her intentions, and her words were the opposite of what Kennedy had implied. But Kennedy was just getting warmed up.

“The CDC and IOM base their defense of thimerosal on these flimsy studies, their own formidable reputations, and their faith that journalists won’t take the time to critically read the science,” Kennedy wrote in 2007 in the Huffington Post, which has emerged as the most prominent online home for cranks of all kinds, particularly people who find scientific research too heavily burdened by facts. “The bureaucrats are simultaneously using their influence, energies and clout to derail, defund and suppress any scientific study that may verify the link between thimerosal and brain disorders… . The federal agencies have refused to release the massive public health information accumulated in their Vaccine Safety Database apparently to keep independent scientists from reviewing evidence that could prove the link. They are also muzzling or blackballing scientists who want to conduct such studies.”

Kennedy has never explained why he thinks the public health leadership of the United States (not to mention its pediatricians) would wish to “poison an entire generation of American children.” He simply wrote that “if, as the evidence suggests,” they had, “their actions arguably constitute one of the biggest scandals in the annals of American medicine.” In his Rolling Stone article, Kennedy ignored the scores of other published reports, few of which were carried out by federal scientists, so that he could focus on the 2004 study produced by the Institute of Medicine, which he attacked mercilessly. Kennedy wrote that vaccines exposed infants to 187 times the daily limit of ethyl mercury determined by the Environmental Protection Agency to be safe. If true, they would all have died at once. Rolling Stone soon printed a correction—and then later corrected that correction. It is impossible to live on the earth and avoid exposure to mercury, but that amount would kill a grown man.

The actual figure was 187 micrograms, which is 40 percent higher than the levels recommended for methyl mercury by the EPA, a tiny fraction of the figure cited in Kennedy’s paper. Throughout the piece, Kennedy confused and conflated ethyl and methyl mercury, quoting as knowledgeable authorities the father-and-son team of Mark and David Geier, who have testified as expert witnesses in vaccine suits more than one hundred times—and who have been reprimanded repeatedly by judges who have dismissed them as unqualified to speak on the subject. (The father has an MD degree; David Geier holds an undergraduate degree in biology.) Their testimony has been tossed out of court on many occasions. One judge called Dr. Geier “intellectually dishonest,” and another referred to him as “a professional witness in areas for which he has no training, expertise, and experience.”

It is important to note that methyl mercury, the compound that is so dangerous when contained in fish and the product of industrial pollution, is not the mercury found in vaccines. The two forms differ by just one carbon molecule, which may seem insignificant. But as Paul A. Offit has pointed out in his indispensable book, Autism’s False Prophets, a single molecule can mean the difference between life and death. “An analogy can be made between ethyl alcohol, contained in wine and beer, and methyl alcohol, contained in wood alcohol,” Offit wrote. “Wine and beer can cause headaches and hangovers; wood alcohol causes blindness.”

Kennedy saw conspiracy everywhere he looked. He has attacked Offit himself, who along with colleagues invented a vaccine to combat rotavirus, which is responsible for killing two thousand children in the developing world every day. Those children typically die of diarrhea, and in June 2009 the World Health Organization recommended that the vaccine be made part of “all national immunization programs.” Kennedy, however, has referred to Offit, who is chief of infectious diseases at the Children’s Hospital of Pennsylvania, as “Dr. Proffit” and as a “biostitute” because he was paid for his research and received royalties from the sale of his invention. Offit, outspoken and unremitting in his support of vaccines, has become a figure of hatred to the many vaccine denialists and conspiracy theorists. He has been threatened with violence so often that congressional aides once warned him not to mention the names of his children in public. For several years, armed guards have followed him to meetings of federal health advisory committees (where he has been called a terrorist), and employees in the mail room at Children’s Hospital routinely check packages or letters addressed to him that look suspicious and might contain bombs.

Meanwhile, data becomes increasingly informative, particularly with regard to the difference between the effects of ethyl and methyl mercury. One of the biggest concerns researchers have always had about mercury was how long it took to be eliminated from a child’s body. In 2008, a team of scientists at the Ricardo Gutierrez Children’s Hospital in Buenos Aires published a report that examined the issue in detail. Kennedy had written that “truck-loads of studies have shown that mercury tends to accumulate in the brains of primates and other animals after they are injected with vaccines—and that the developing brains of infants are particularly susceptible.” It turns out that mercury in vaccines can be tolerated in far larger doses than was previously understood. More than two hundred children were studied after receiving vaccines that contained ethyl mercury, which is still used routinely in Argentina. The children excreted half the mercury within four days, and their levels returned to normal eleven days after vaccination. In contrast, it takes roughly seventy days for the body to flush half of a dose of methyl mercury.

No scientific report has seemed able to temper Kennedy’s ardor or that of people like the actress Jenny McCarthy and her boy-friend, Jim Carrey, who have become America’s marquee vaccine protestors. Like Kennedy, McCarthy knows how to wield her celebrity; in the fall of 2007 she appeared on Oprah Winfrey’s television show, unleashing what she referred to as her “mommy instinct” in search of the cause of autism. “What number will it take for people just to start listening to what the mothers of children with autism have been saying for years—which is we vaccinated our babies and something happened. That’s it,” she said. When confronted with data from the Centers for Disease Control that seemed to provide scientific refutation of her claims, McCarthy responded, “My science is named Evan [her son] and he’s at home. That’s my science.” McCarthy says that she “fixed” Evan by changing his diet, and recommends that other “warrior moms” do the same. She is fond of saying that she acquired her knowledge of vaccinations and their risks at “the University of Google.”

Like Kennedy, McCarthy and Carrey contend that the federal government and pharmaceutical companies have conspired to keep the evidence that thimerosal-containing vaccines cause autism a secret. “In this growing crisis,” Carrey wrote in the Huffington Post in April 2009, “we cannot afford to blindly trumpet the agenda of the CDC, the American Academy of Pediatrics (AAP) or vaccine makers. Now more than ever, we must resist the urge to close this book before it’s been written. The anecdotal evidence of millions of parents who’ve seen their totally normal kids regress into sickness and mental isolation after a trip to the pediatrician’s office must be seriously considered.”

He had a point: every parent with an autistic child has the right to demand that federal researchers seriously consider anecdotal evidence. Anything less would be disgraceful. And that is why it has been considered in dozens of studies over more than a decade. Continuing to encourage false hope in this way, however, is an approach that Kathleen Seidel, whose blog Neurodiversity is the most complete and accessible collection of useful information about autism, has described quite accurately as nonsense, a litigation-driven hypothesis that autism is a consequence of vaccine injury.

Conspiracy theories are like untreated wounds. They fester and deepen—and the autism-vaccine conspiracy is no exception. Within days of Carrey’s article, thousands of people had responded with comments on the Huffington Post Web site. Most were positive. Barbara Loe Fisher of the National Vaccine Information Center refers to the Public Health Service’s insistence that the benefits of vaccines outweigh their risks as the “great denial”: “It is only after a quarter century of witnessing the Great Denial of vaccine risks,” she wrote, “which has produced millions of vaccine damaged children flooding special education classrooms and doctors offices, that the magnitude of that unchecked power has been fully revealed.” Clearly, she is right about the powerful strain of denialism that the struggle over vaccines has exposed. She has the denialists and realists confused, however. That is one of the problems with conspiracy theories. After enough distortions seep into conventional thought, “the facts” look as they would in a funhouse mirror. Just tune in to YouTube and check out Robert F. Kennedy Jr. on the subject of vaccines. In June 2008, at a rally on Capitol Hill to “Green Our Vaccines”—in other words, to make them environmentally safe—Kennedy delivered his most inflammatory speech on the subject, saying that the “thimerosal generation is the sickest generation in the history of this country.” It is not clear how he arrived at that conclusion, since life expectancy for newborns in the United States has increased dramatically over the past seventy years, from 57.1 for babies born in 1929 to 77.8 for babies born in 2004.

The change has been significant even during the past fifteen years—when Kennedy argues children have suffered the most. The trend is the same with regard to DALYs, or disability-adjusted life years, which measure healthy life expectancy—the number of years a child is likely to live without losing time to disability and sickness. In addition, during the period between 1990 and 2004, Kennedy’s key danger years, childhood cancer death rates fell sharply (among both sexes, all ethnic groups except American Indians, and in every census region of the United States). It would be difficult to argue that any generation of children in the history of the world has ever been as healthy as the “thimerosal generation.”

Yet, that sunny day in June, more than a thousand activists, most from groups like Talk About Curing Autism (TACA), Generation Rescue, Healing Every Autistic Life, Moms Against Mercury, and Safe Minds, a nonprofit organization that falsely characterizes autism as “a novel form of mercury poisoning,” listened as Kennedy described the vaccination polices of the United States government as the “worst crime since the cover-up of the Iraq war,” and added that the “the treatment of these children and the cost to our society” would far exceed the cost of the war itself.

DOES KNOWLEDGE SIMPLY disappear over time? After centuries of scientific progress have we not constructed pyramids of information solid enough to withstand periodic waves of doubt and anxiety? Human history has repeatedly suggested that the answer is no, but it isn’t ignorance that makes people run from the past or shun the future. It’s fear.

In 1421, China was far ahead of the rest of the world in sophistication, in learning, and particularly in scientific knowledge. It was the least ignorant society on earth. Then the newly completed Forbidden City was struck by a lightning bolt just as it opened, and the emperor reacted with horror. He interpreted the lightning as a sign from the gods that the people of the Middle Kingdom had become too dependent on technology—and were not paying enough attention to tradition or to the deities. So, as Gavin Menzies describes in his book 1421: The Year China Discovered America, the Chinese burned every library, dismantled their fleets, stopped exploring the globe, and essentially shut themselves off from the outside world. The result? A downward spiral that lasted for five centuries. Japan, too, recoiled at progress by giving up the gun in the seventeenth century. Until they did, they were better at making steel than any Western country, and their weapons were more accurate, too. The samurai despised firearms. To them, they were nothing more than killing machines with the potential to destroy an enduring way of life. When somebody pulls a gun, it no longer matters how honorable you are or how many years you have trained with a sword. Guns put the social order in jeopardy, so Japan banned and eventually melted them all. The gears of social mobility were jammed into reverse. Again, it took centuries for Japan to regain its technological supremacy.

The history of vaccines, and particularly of smallpox, is filled with similar stories of fear at war with progress. According to Voltaire, the ancient Chinese inhaled dried powder of smallpox crusts through the nose in a manner similar to taking snuff. Thomas Jefferson’s children were vaccinated by a slave who learned how to do it as a traditional aspect of African medicine. “We keep forgetting this stuff over and again,” Juan Enriquez told me. Enriquez, who founded the Life Sciences Project at the Harvard Business School, is one of America’s most insightful genomic entrepreneurs, and has spent many years studying the unusual ebb and flow of knowledge. “People become scared of change,” he said. “They get scared of technology. Something bad happens and they don’t know how to react: it happened with the emperor in China, and with smallpox, and it has happened with autism, too. People want to blame something they can’t understand. So they blame technology. And we never stop forgetting how often this happens. We think of technology and the future as linear. It so clearly is not.”

The controversy surrounding the MMR vaccine and autism is far from the first time the world has recoiled from vaccination, with at least some people convinced it does more harm than good. Smallpox arrived in Boston in 1721, carried by passengers on a ship from the Caribbean. It was the second coming of the epidemic to American soil—the first had landed more than one hundred years earlier. This outbreak was more severe, though, and by the time it had run its course, half of the ten thousand residents of Boston had fallen ill, and more than a thousand had died. Cotton Mather, the fiery, brilliant, and unpleasantly self-righteous preacher, had heard about vaccination several years earlier from an African slave. He then read about the practice in a British scientific journal and became convinced it could provide the answer to the plague that threatened the city (and the entire New World). Mather attempted to interest the town’s residents in what he acknowledged was the genuinely risky “Practice of conveying and suffering the Small-pox by Inoculation,” a practice “never used … in our Nation.”

There were few takers. Instead, the majority of the population was awed by the ability of smallpox to wipe out entire nations and wondered whether it was not simply a judgment from God, rather than a disease one could defeat with medicine. Most people condemned inoculation. Perhaps the answer was to turn inward, to pray more fervently. Mather screamed from the pulpit (joined by several others, including his father, Increase Mather—they came to be known as the Inoculation Ministers). They faced opposition from the nation’s first powerful newspaper, known at the time as the New England Courant (eventually to become the Hartford Courant), which was published by Benjamin Franklin’s brother James—and not just from him. “Cotton Mather, you dog, damn you! I’ll inoculate you with this; with a pox to you,” said a note that was attached to a bomb lobbed into Mather’s house. All because he argued for the adoption of the most important public health measure in the history of colonial America.

Ben Franklin himself opposed the idea of the inoculation—called variolation, in which healthy people would have pus from the scabs of smallpox victims rubbed onto their skin. This usually produced a much milder form of smallpox, although a small percentage of the people vaccinated in this way died as a result. When the final tally was made, however, the salutary effects of vaccinations were impossible to deny. Of the 240 people inoculated during the epidemic in Boston, six died, one in forty. Among the rest of the population the mortality rate was one in six. Even those made sick by the vaccine tended to become less seriously ill than those who acquired the infection in the usual way.

Years later, Franklin’s son died of smallpox, after which he became an ardent supporter of vaccination. He even made a special appeal to parents who might be afraid of the consequences. “In 1736 I lost one of my sons, a fine boy of four years old, by the smallpox taken in the common way,” he wrote in his autobiography. “I long regretted bitterly and still regret that I had not given it to him by inoculation. This I mention for the sake of the parents who omit that operation, on the supposition that they should never forgive themselves if a child died under it; my example showing that the regret may be the same either way, and that, therefore, the safer should be chosen.” George Washington initially hesitated to vaccinate his Continental Army troops during a smallpox outbreak, writing that “should We inoculate generally, the Enemy, knowing it, will certainly take Advantage of our Situation.” By 1777, however, he ordered mandatory vaccination for every soldier.

Vaccines work primarily by stimulating the immune system to produce a defensive response; there is a small risk that the response won’t be good enough and the vaccine will cause the disease it has been designed to prevent. Unless you compare those risks with the alternative—that is, of not having the vaccine at all—there is no way to properly judge any vaccine’s value to society. It has been three hundred years since Tony Blair’s distant predecessor, Robert Walpole, Britain’s first prime minister, purchased vaccines for the children of King George I. “Here is the tradition that Tony Blair is fighting against,” Enriquez said. We were sitting in the parlor of his house outside Boston—which had once served as a stop along the Underground Railroad. Enriquez is a collector of medical records, scientific charts, and many types of maps. On the table before us he had spread his “smallpox collection,” letters relating to the history of the disease. He produced a yellowed parchment that looked more like an eighteenth-century proclamation than a bill. “This is from a guy called Charles Maitland, a surgeon,” he said. “It’s a bill of sale for vaccinating the king’s children in 1724, signed by Walpole. So here is the British royalty in 1724 understanding that it is really important to vaccinate your children. It is just amazing to me that you can take this … and move to where we are today.”

At that, Enriquez stood up to fetch another armful of documents. “These are Jenner’s notebooks on vaccination,” he explained. Edward Jenner is generally credited with having invented the smallpox vaccine, after noting that milkmaids rarely got the disease. He theorized, correctly as it would turn out, that the pus in the blisters that milkmaids received from cowpox (a disease similar to smallpox, but much less virulent) protected them from smallpox. “Here are the letters to the public health department in 1804 donating the skins that Jenner had tested. And here are the enclosed tests.” It was all there: the data, the evidence, sitting irrefutably three centuries later on a table in a suburb of Boston. “We have this science,” Enriquez said, pointing respectfully at the notebooks. “Look at the data, it’s so clear. Here is the result of the first twenty tests. It’s a pile of stuff telling us something the king and his circle knew instinctively in 1724: vaccinations are essential.”

Instincts evolve. We have become inherently suspicious of science, so when a drug company or a researcher does something wrong, fails to show data that could be harmful, for example, or when there’s an issue having to do with the safety of a particular product, it feeds into the underlying suspicion and permits people to say, “Ah! All of science is bad.” When people encounter something that isn’t immediately explicable—autism, for example—it plays into this sense of doubt, and even when the scientific evidence is overwhelming people don’t always believe it. It is a climate that has created people like Tony Blair’s wife, Cherie, who has long been known for her skepticism toward many aspects of conventional medicine. She recently acknowledged that while she had been highly suspicious, she did eventually vaccinate her son Leo. Blair had been influenced by, among others, a half sister who had criticized the bonus payments doctors in England received for administering MMR shots, and publicly declared that she would never vaccinate her own daughter. “A number of people around me, whose views I respected, were vociferously against all forms of vaccination,” Blair said in 2008. “Over the years I had listened to their side of the argument and, it’s fair to say, I was in two minds.”

INCREASINGLY STYMIED in their quest to blame autism on the mercury contained in thimerosal, or on vaccines in general, unconvinced by mounting evidence that genetics and the environment play significant roles in the development of autism, activists began to hunt for a new approach to bolster their vaccine theory. On March 6, 2008, they found what they were looking for. On that day, the parents of Hannah Poling, a nine-year-old girl from Athens, Georgia, held a press conference to announce that the Department of Health and Human Services had issued what Jon Poling, the girl’s father, referred to as a ruling that may “signify a landmark decision with children developing autism following vaccines.” He said he made the public statement to provide “hope and awareness to other families.” His lawyer, Clifford Shoemaker, who has turned the vaccine plaintiff industry into a lucrative career, was by his side. They both nodded when a reporter asked whether the case was the first in which “the court has conceded that vaccines can cause autism.”

Nearly five thousand families have similar suits before the court, so any judgment that applied broadly would have had profound implications. Paul Offit has described Hannah Poling’s case in the New England Journal of Medicine: “Hannah Poling received five vaccines when she was nineteen months old—diphtheria- tetanus-acellular pertussis, Haemophilus influenzae type b (Hib), measles-mumps-rubella (MMR), varicella, and inactivated polio. At the time, she was a typically playful and communicative girl. Within two days she had become lethargic, irritable, and febrile. Ten days after vaccination, she developed a rash consistent with vaccine-induced varicella. Months later, with delays in neurologic and psychological development, Hannah was diagnosed with encephalopathy,” a syndrome characterized by altered brain function, “caused by a mitochondrial enzyme deficit,” which left her weak and often confused. Hannah’s symptoms included problems with language, communication, and behavior—all features of autism spectrum disorder. Although it is not unusual for children with cellular disorders like mitochondrial enzyme deficiencies to develop neurologic symptoms between their first and second years of life, Hannah’s parents believed that vaccines had triggered her encephalopathy. That’s why they sued the Department of Health and Human Services for compensation under the National Vaccine Injury Compensation Program. When a federal court awarded damages to their daughter, the vaccine scare was ignited anew.

The vaccine court is unlike any other in the United States, however, and the suit can only be examined in the context of the way it works. In the late 1970s and early 1980s, American lawyers successfully sued pharmaceutical companies, claiming that vaccines for pertussis caused a variety of illnesses, including unexplained coma, sudden infant death syndrome, Reye’s syndrome, mental retardation, and epilepsy. As a result, by 1986 all but one manufacturer of the diphtheria-tetanus-pertussis vaccine had abandoned the American market. The risk of lawsuits became far greater than the potential for profits. The federal government, increasingly concerned that no company would be willing to manufacture essential vaccines, passed the National Childhood Vaccine Injury Act, which included the creation of the VICP.

Funded by a federal excise tax on each dose of vaccine, the VICP compiled a list of compensable injuries. If scientific studies supported the notion that vaccines caused an adverse event—such as thrombocytopenia (the dangerous depletion of platelets) after receipt of measles vaccine, or paralysis following an oral polio vaccine—children and their families were compensated, and usually quite generously. The average family received nearly $1 million. Health officials developed a table of injuries that would apply, and the number of lawsuits against vaccine manufacturers fell dramatically. One of those “table injuries,” encephalopathy following a measles vaccine, is the cellular disorder for which Hannah Poling was awarded money.

Because some of the court records are sealed, it is impossible to know with certainty how the decision was made. Nonetheless, Hannah’s father, Jon Poling, and Shoemaker, the lawyer, were wrong: neither the court nor the federal government conceded that vaccines cause autism. They conceded that in that specific case vaccines may have been responsible for exacerbating a condition with symptoms that are similar to those of many autistic disorders. Hannah had a mitochondrial enzyme deficiency, which consisted of a metabolic disorder called encephalopathy. (Mitochondria are responsible for producing 90 percent of the energy we need to stay alive. Many defects can prevent them from functioning properly or at all—and without enough energy, cells, like any other factory, stop working.)

The court was compelled to address a difficult question: could the fever that Hannah developed following those vaccines (one of which was a measles vaccine) worsen her encephalopathy? “This is a particularly complex issue,” Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Diseases, told me. “And it’s even more complicated by the fact that it is likely that there are a minute fraction of kids who have an underlying defect—clearly, mitochondrial defects are the one that stands out—where at a certain time of their life, when they get confronted with an influenza, with an [environmental toxin] or a vaccine, it’s going to accelerate what already was going to happen anyway. Then some people will say that every autistic kid became autistic because of a vaccine. And we know absolutely that that’s not the case.”

In early 2009, the vaccine court agreed. After ten years of bitter scientific and legal battles, the court rejected any relationship between autism and vaccines. “Petitioners’ theories of causation were speculative and unpersuasive,” wrote Special Master Denise Vowell in the case of Colten Snyder v. HHS. “To conclude that Colten’s condition was the result of his MMR vaccine, an objective observer would have to emulate Lewis Carroll’s White Queen and be able to believe six impossible (or at least highly improbable) things before breakfast.”

It was a decisive victory for science—but denialists have no interest in scientific decisions. “The vaccine court was wrong,” Jay Gordon wrote on the Huffington Post the next day about the nearly thousand pages’ worth of rulings in three cases. Gordon, or Dr. Jay as he calls himself, is read by many people and serves as, among other things, Jenny McCarthy’s pediatrician. He added, “Let me state very simply, vaccines can cause autism… . The proof is not there yet. It will be found.” His judgment on the court and the ruling was equally certain. “They were disdainful and unscientific in their approach and did not gather the needed evidence… . Vaccines as they are now manufactured and administered trigger autism in susceptible children.” (While rejecting scientific evidence themselves, denialists often explain their position by citing the “unscientific” approach of opponents.)

Nobody can blame any parent of an autistic child for skepticism, confusion, or anger. But when confronted with statements like Gordon’s, an honest researcher could only shake his head in wonder. “If it wasn’t for suspicion about science, I think the lack of that computing rationally would dawn on people,” Fauci said. “This is ridiculous! You have all these studies, you have this, you have that, it doesn’t matter. And it’s a combination of the underlying mistrust and the fact that people with autistic children see them suffering horribly and they need an explanation. What’s the explanation? Well, we don’t have one. Instead we have fear, and fear is what propels this movement.”

Because Hannah Poling’s encephalopathy included features of autism, it raised questions about how autism is defined and why case numbers have expanded so rapidly. Many reasons seem to have converged: new and broader diagnoses for Medicaid and insurance, increased awareness, and more access to services are all among them. The federal Individuals with Disabilities Education Act, passed in 1991, guarantees appropriate public education for children with autism. Soon after the law was enacted, schools began reporting an increase in the number of autistic students. That is one reason the act was written, but to receive special education a child must have a specific diagnosis. In the past, parents without a clear sense of what was wrong with their children were often vague. They had no choice, because states presented few options. Autism now appears on application forms for state aid, and it is one of the categories parents can consider when seeking special educational support.

Once again, the confusion surrounding the Poling decision was magnified by the Internet, causing a new wave of fear, anxiety, and, naturally, reluctance on the part of many parents to vaccinate their children. It also played into the anti-vaccine movement’s newest catch-phrase: “Too Many Too Soon.” The phrase implies that there are all sorts of toxins in our vaccines and that by receiving so many shots at such an early age, children’s immune systems are easily overcome. Now that thimerosal has proven ineffective as a propaganda weapon, the anti-vaccine forces have begun more frequently to invoke “Too Many Too Soon” and “Green Our Vaccines” as standard tropes.

As David Gorski, a surgeon who teaches at the Wayne State University School of Medicine, has pointed out in the blog Science-Based Medicine, they are brilliant slogans. Who doesn’t want a green vaccine? Jenny McCarthy likes to say she is not opposed to vaccines, just to the poisons they contain. “This is not an anti-vaccine rally or an anti-vaccine group,” she said at the Green Our Vaccines Rally in Washington in 2008. “We are an intelligent group of parents that acknowledges that vaccines have saved many lives, but what we’re saying is that the number of vaccines given [needs to be reduced] and the ingredients, like the freakin’ mercury, the ether, the aluminum, the antifreeze need to be removed immediately after we’ve seen the devastating effect on our children.

“I know they are blaming me for the measles outbreak and it cracks me up,” she continued. “What other consumer business blames the consumer for not buying their product? It’s a shit product. Fix your product. That’s what they are trying to do: scare people into vaccinating again and point the blame.” In April 2009, McCarthy and Carrey began a national tour to promote her third book on autism, Healing and Preventing Autism: A Complete Guide, written with McCarthy’s “biomedical” adviser, Dr. Jerry Kartzinel. Larry King has always been among McCarthy’s most enthusiastic enablers, and he was one of the couple’s first stops on the tour. King asked McCarthy why she thought pharmaceutical companies would expose children to so many shots and such danger. “Greed,” she said, making note of the increased number and type of vaccinations in the past twenty years. King asked: because they all want to make money? “Of course,” McCarthy replied.

That week, in an interview with Time magazine, McCarthy actually said she thought that old diseases would have to return—as in fact they have. “I do believe sadly it’s going to take some diseases coming back to realize that we need to change and develop vaccines that are safe. If the vaccine companies are not listening to us, it’s their fucking fault that the diseases are coming back. They’re making a product that’s shit. If you give us a safe vaccine, we’ll use it. It shouldn’t be polio versus autism.” As she has repeatedly, McCarthy cited the number of vaccines children receive as a large part of the problem.

Nobody can dispute that the number of vaccines has multiplied enormously. One hundred years ago children received a single vaccine: smallpox. By 1962 that number had grown to five (diphtheria, pertussis, tetanus, polio, and the MMR). Today children are vaccinated for eleven diseases, and by their second birthday that can entail as many as twenty separate shots. Yet because molecular biology has made it possible to create vaccines with fewer antigens, children are exposed to far less of a burden than children in past generations had been. The smallpox vaccine, for example, contained two hundred proteins—all separate molecules. Together, the eleven vaccines that children routinely receive today contain fewer than 130. The bacteria that live on the nose of a newborn child or the surface of their throat number in the trillions. “Those bacteria have between 2,000 and 6,000 immunological components and consequently our body makes grams of antibody to combat these bacteria… . The number of immunological challenges contained in vaccines is not figuratively, it is literally, a drop in the ocean of what you encounter every day,” Paul Offit has written.

The Poling decision opened the door to a new round of debates, and one of the first to rush through it was Bernadine Healy, a former director of the National Institutes of Health. She stunned parents and scientists alike in 2008 by saying that while “vaccines are safe, there may be this susceptible group. I think that public health officials have been too quick to dismiss the hypothesis as irrational.” That year, the anti-vaccine blog the Age of Autism, which describes itself as the “daily web newspaper of the autism epidemic,” made Healy its person of the year. She often tries to present herself as a calm voice of reason caught between two equally emotional camps. Following Jenny McCarthy’s appearance on Larry King Live in 2009, however, Healy ventured even deeper into denialism. “The work is long overdue; shockingly, so is a study comparing groups of vaccinated and unvaccinated children,” she wrote on the blog she maintains for U.S. News and World Report. Actually, those studies, involving more than a million children, have been carried out in several countries and for many years.

“How many studies are enough?” Fauci asked. “The Institute of Medicine did all it could do. But the real problem here is that no politician can afford to appear as if he or she is brushing off the agonizing concerns of a parent with an autistic child. So none would say what needed to be said. I would have liked to have seen some political leaders say, Folks, come on,” Fauci said. “We’re going to put fifty million more dollars into autism research and look at what the real causes might be. But it’s dangerous politically to do that, because of the intensity of the people who believe that vaccines are the problem. When you have a suffering family, and an innocent kid who’s got a life that is going to be difficult, it’s very, very tough to go and make a pronouncement that this is not the case. Particularly because you will then have that rare event when a vaccine might precipitate an underlying genetic defect that might just as well have been set off by something else, like the flu. It’s just dangerous politically for anybody to speak out. It’s not very courageous not to do it, but when political people look at all the things they’re going to step up to the plate on, that’s not one of them.”

IT’S HARD TO GET to Marie McCormick these days. You have to make it past two guards at the entrance of her building at the Harvard School of Public Health. There is another guard not far from her office. Most of the time, she lets assistants answer the phone, and she sends a lot of e-mail to the spam box, too. McCormick has been subpoenaed to appear in a vaccine compensation case—not an occurrence she envisioned when she took the position as head of the Institute of Medicine’s Immunization Safety Review Committee. She remains cheerful and committed to her work, yet she and other public health officials have watched as a steady stream of troubling facts emerged over the past decade: more parents are choosing to homeschool their children, and while that is usually for economic or religious reasons, surveys suggest that an increasing number of parents do it because vaccinations are not mandated for most children schooled at home.

In Ohio, for example, the number of religious and philosophical exemptions for vaccines nearly quadrupled between 1998 and 2008, from 335 to 1,186. (In most states, though, it is actually easier to get exemptions from vaccine requirements than to have your child vaccinated.) Maine led the nation in immunizing children in 1996 with a compliance rate of 89 percent. By 2007, that figure had fallen to just 72.9 percent. The numbers vary widely even within states. On Vashon Island, an upscale suburb of Seattle, nearly 20 percent of parents have opted out of vaccination, and as the number of exemptions grows, infectious disease proliferates. In early 2009, after a lengthy investigation, the Los Angeles Times found that while the California state exemption rate was only 2 percent, the bulk of those exemptions were clustered in just a few school districts.

The trend lines are clear. In 1997, 4,318 California kinder gartners entered school with vaccine exemptions. By 2008 the number—with fewer students enrolled—had more than doubled. At Ocean Charter School near Marina del Rey, 40 percent of kin dergartners entering school in 2008 and 58 percent entering the previous year were exempted from vaccines, among the highest rates in the nation. These numbers are particularly discouraging because they threaten herd immunity. The term refers to the fact that if you are unvaccinated and everyone around you—the herd—is, there would be nobody who could conceivably spread the illness. The herd would protect you. When vaccination rates drop significantly below 90 percent, however, herd immunity begins to disappear and infectious diseases can spread. Without herd immunity, math takes over, and the results are easy to predict. The winter after Wakefield’s Lancet article appeared, for example, more than one hundred children were hospitalized in Dublin, three of whom died. Until that year, Irish public health officials regarded measles as a disease that had essentially been eradicated.

Viruses are tenacious and they multiply rapidly; without vigilance, past successes are quickly erased. By June 2008, as a result of the declines in vaccine coverage, measles became endemic in the United Kingdom fourteen years after it had practically vanished. That means that for the foreseeable future the disease will recur with predictable regularity. Since April 2008, two measles-related deaths have been reported in Europe, both in children who, due to congenital illnesses that affected their immune systems, were unable to receive the MMR vaccine. Children like that depend on herd immunity for protection from an infectious disease like measles, as do children under the age of one, who normally are too young to have received the vaccine. Unless the vast majority of children are vaccinated, herd immunity disappears.

It is a remarkable fact that measles is on the rise in countries like Britain and the United States even as death rates have plummeted over the past five years in the developing world. The United States had more measles infections in the first half of 2008 than in any comparable period for nearly a decade. There are regions where half the children remain unvaccinated. Measles is particularly virulent and moves rapidly. “Somebody who has taken an exemption from school laws, like a philosophical or religious exemption, is thirty-five times more likely to get measles … and twenty-two times more likely to get whooping cough,” said Dr. Lance Rodewald, director of the Centers for Disease Control’s Immunization Services Division. Usually in the past, deaths began to occur when the caseload reached into the hundreds. Many public health officials feel that is now inevitable.

The threats are not theoretical—nor are they confined to measles. Early in 2009, five children fell ill after an outbreak of Hib influenza (Haemophilus influenzae type B) in Minnesota. One of the children died—the first Hib fatality in the state since 1991, the year after a vaccine became available. Until then, severe Hib infections would typically sicken twenty thousand children under the age of five every year in the United States, resulting in about a thousand deaths. Of the five Minnesota cases, three—including the child who died—were infants whose parents had refused to vaccinate them.

There has been a concerted international effort, led by the Bill and Melinda Gates Foundation and the World Health Organization, to eradicate polio. But success has been elusive, largely because of opposition to vaccines in northern Nigeria. In the summer of 2003, Muslim clerics banned polio vaccinations, claiming that the drugs were a Western plot to spread HIV and sterilize Muslim girls. People stopped taking the vaccine, and the results were disastrous: HIV rates didn’t change but polio infections rose rapidly; some of those people traveled to the hajj in Mecca, infecting others. Soon there were cases in a dozen other countries. A world on the verge of eradicating polio would have to wait for another day. “Never forget that the longest flight any person can take anywhere in the world is shorter than the shortest incubation period of an infectious disease,” McCormick said. “So you really have to understand that it is not only possible, but inevitable, that if people aren’t vaccinated they will get sick.”

Nearly every vaccine is under some form of attack. In 2007, the conservative legal group Judicial Watch announced that it had uncovered three deaths linked to the human papilloma virus (HPV) vaccine, which has been the subject of much debate around the country as states decide whether to require vaccinations before permitting girls to enter sixth grade. HPV is the most common sexually transmitted disease in the United States; at least half of all sexually active Americans become infected at some point in their lives. The virus is also the primary cause of cervical cancer, which kills nearly five thousand American women every year and hundreds of thousands more in the developing world.

The vaccine has proven exceptionally effective at preventing those infections. But Judicial Watch’s report was picked up throughout the country (and the world) and often reported as if it were true. Each death was registered in the Vaccine Adverse Events Reporting System (VAERS), and each concluded that the girls died of heart attacks after receiving the HPV shots. When officials from the Centers for Disease Control talked to doctors and examined the dead girls’ medical charts, however, they found that one death, a case of myocarditis, was caused by influenza virus. The other two were a result of blood clots in adolescents taking birth control pills, which are known to raise the risk of blood clots. “These deaths are tragic, but appear to have causes unrelated to vaccination,” said Dr. John Iskander, co-director of the Immunization Safety Office at the CDC. Nonetheless, another front in the war against progress had been opened, and there have been other attempts to dismiss the importance of this new and effective cancer vaccine.

Perhaps that should surprise no one, since the fear of a common disease like autism will almost always outrank a fear about something like measles that people no longer take seriously. “Most parents I know will take measles over autism,” J. B. Handley said not long ago when asked, for perhaps the thousandth time, why he persists in opposing the MMR vaccine. Handley is founder of Generation Rescue, an organization of parents who remain strongly committed to the idea that vaccines cause autism. Is that really a choice we are prepared to let him make? By choosing not to vaccinate their children, parents are not protecting them from autism—as so many epidemiological studies have demonstrated. They are simply putting their children—and the children of their neighbors—at greater risk of contracting diseases that could send them to the hospital or worse. How many American children will have to die in order to make the point that vaccinations are vital? How far will we descend into denialism before the fear of disease once again overshadows the fear of vaccines?