In February 1998, British physician Andrew Wakefield and 12 colleagues published a study of 12 autistic children in the prestigious medical journal Lancet. At a dramatic press conference, Wakefield declared that the combined measles, mumps, and rubella (MMR) vaccine was the likely cause of autism in eight of the children. Noting intestinal abnormalities in the subjects, he suggested that the measles vaccine virus had traveled to the children’s intestines and brought on infection and inflammation, allowing harmful proteins to enter the bloodstream and cross the blood-brain barrier, causing autism. Based on all this, Wakefield recommended that the different components of the MMR vaccine be administered separately. In practice, this meant that children wouldn’t get vaccinated at all if their parents refused the combination dose.

His claims, linked to so prestigious a journal, caused an immediate sensation. The spirit of public reaction was captured by the 2003 British television drama Hear the Silence, which depicted Wakefield as a heroic figure helping a mother find the true cause of her son’s autism. Unethical drug company executives and public-health officials were the film’s villains. This fictive Wakefield faced harassment and intimidating phone calls. His files were stolen, but he persisted in his important work.

British parents paid attention. MMR immunization rates in England dropped from almost 90 percent to 70 percent following Wakefield’s presentation, with markedly lower rates in specific areas. Local measles outbreaks soon followed. Wakefield also attracted a large following among parents of autistic children in America and around the world. In the year 2000, he testified in an odd House committee hearing chaired by Indiana Republican Dan Burton, who was apparently convinced that vaccines had caused his grandson’s autism.

Today, no serious medical or scientific expert believes that vaccines cause autism. Yet many nervous parents continue to think otherwise. One of these is actress and model Jenny McCarthy. During a 2007 “Oprah” appearance, she said that not long after her son received his shot, “The soul was gone from his eyes.” When Oprah asked what McCarthy knew about vaccine science, McCarthy responded, “My science is Evan, and he’s at home. That’s my science.” Winfrey said, “Thank God for Google,” to which McCarthy responded, “The University of Google is where I got my degree from.”

As in England, increasing numbers of parents in the United States chose not to immunize their children—for measles, mumps, and rubella, and for other diseases, too. As in England, outbreaks of vaccinatable diseases have re-emerged as a public health problem. In 2005, an unvaccinated Indiana teen was exposed to measles on a church mission to Romania. She exposed 500 others at a church picnic, infecting 31 out of the 35 unvaccinated picnickers. Of the remaining 465 immunized people, only three were likewise infected. In California last year, the state recorded thousands of cases of pertussis (whooping cough) and nine related deaths, the most in decades. In 2009, Australia saw a record 13,000 cases. How is it that in 2011 we are faced with significant, sometimes lethal outbreaks of such readily prevented diseases?

That is the subject Paul Offit and Seth Mnookin investigate in their recent books. Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia, chronicles several such outbreaks in Autism’s False Prophets and Deadly Choices. Science reporter Mnookin, a contributing editor at Vanity Fair, covers much of the same material in The Panic Virus.

These authors tell depressingly similar stories. Sloppy or fraudulent scientists combine with like-minded parent-activists to spread false rumors, leading hundreds of thousands of parents not to follow public-health recommendations. The combination of public complacency, general ignorance and gullibility, and widespread distrust of pharmaceutical companies and scientific medicine created massive opportunities for anti-vaccination activists to do great harm. How should the medical and public-health communities address this problem? How should progressives respond when their respect for parental autonomy collides with their pursuit of public health and respect for legitimate expertise?

Why do so many people buy into readily debunked vaccine-autism claims spread by people who regularly turn out to be charlatans or grossly wrong? In part, this troubling trend is an ironic consequence of vaccines’ very success in protecting public health. Millions of older people remember terrified parents refusing to let their kids use the local swimming pool. They remember polio patients in iron lungs. Today we don’t experience the palpable fear that polio and other diseases ostensibly vanquished by vaccines once evoked. Complacency is the predictable result.

Part of the answer has to do with the nature of autism. Autism spectrum disorders (ASDs) are a frightening, sometimes mysterious set of social, communication, and behavioral challenges. Signs of an ASD often emerge in toddlers who appear to have been developing appropriately, yet who for no apparent reason begin to seem more withdrawn, behave strangely, or become unresponsive to usual social cues. An ASD is sometimes first diagnosed or suspected around the time a child receives her first doses of the combined MMR or the diphtheria-pertussis-tetanus (DPT) vaccines, around one year of age. Many parents then draw the obvious, statistically erroneous conclusion. Given improved diagnostic methods, greater public awareness, and an expanding range of autism-labeled disorders, the annual rate of ASD diagnoses has also increased, reaching a level of as many as one in every 100 children. No reliable data exist to indicate whether this trend reflects a true increase in underlying disease prevalence or is entirely explained by increased detection and labeling. The fact that this trend coincides with a steadily expanding vaccination schedule reinforces public concerns.

Several biological pathways have been proposed between vaccines and autism, none supported in the epidemiological record. Perhaps the most explosive theories concern a mercury-based preservative called thimerosal, which was used to prevent bacterial contamination in some vaccines. Concerns about thimerosal emerged during the 1990s. Although there were no known epidemiological harms, respected pediatrician Neal Halsey became concerned about infants’ cumulative exposure. He sounded the alarm within the elite world of pediatricians and public-health professionals concerned with vaccine safety. Seeking to be candid, proactive, and reassuring, the American Academy of Pediatrics and the Public Health Service issued a 1999 statement, saying there was no evidence that thimerosal caused harm but recommending that it nonetheless be shelved. Unfortunately, this measured statement did more to frighten and confuse people than to assuage public doubts.

That 1999 statement also produced tragic unintended consequences. For example, it was safe to delay hepatitis B vaccines for infants, as long as their mothers were not infected. But as Offit relates in Autism’s False Prophets, 10 percent of all hospitals, “frightened by the notion of giving a thimerosal-containing vaccine to newborns, ignored recommendations and simply suspended the hepatitis B vaccine for all newborns.” One infant in Michigan died. Halsey and public-health authorities, Offit writes, “set sail on a grand experiment, believing that the harm caused by thimerosal was greater than the harm caused by disrupting the hepatitis B immunization program.”

Studies in several countries find no correlation between the introduction or removal of thimerosal and population autism rates. In 2003, it was shelved in the United States for infant vaccines. The next year, an Institute of Medicine (IOM) expert panel released a definitive report indicating no evidence of harm from thimerosal. Certainly since then, there has been no genuine scientific controversy regarding these concerns. However, many parents never accepted these findings, and indeed directed great anger and suspicion at the IOM itself. Committee members received hate mail and threats, some requiring police intervention.

Offit is no mere onlooker in this story. He is a long-time pediatrician who developed a rotavirus vaccine and his expertise shows, particularly in highlighting the epidemiological or biological implausibility of posited vaccine-related harm. He is also an angry writer, which is not surprising given the harassment he has endured from anti-vaccine activists because of his emphatic views, and perhaps because he holds a lucrative patent on that rotavirus vaccine. In the prologue of Autism’s False Prophets, he recounts a phone call he received from a man who began by assuring Offit that both of them wanted what was best for their children—but then seemed to threaten Offit by listing his children’s names and ages and where they went to school.

Offit’s targets generally deserve the drubbing. Unethical or incompetent scientists, greedy lawyers, and ignorant activists roam his pages. By his account, a small but pernicious industry of expert witnesses and personal-injury lawyers did great damage to the American vaccine industry until the mid-1980s, when the National Childhood Vaccine Injury Act took most vaccine litigation out of state courts into the jurisdiction of special federally appointed judges, who quickly compensated the parents of infants and children who report any condition on a list of known or suspected vaccine-related harms. The act imposed a lower standard of proof, lower legal expenses, and smaller dollar awards, and stabilized the vaccine industry.

Offit is drawn to libertarian proponents of tort reform such as the Cato Institute’s Walter Olson. He chides Democrats for being too cozy with personal-injury lawyers. Autism’s False Prophets devotes six pages to dubious silicon breast implant litigation that bankrupted Dow Corning. In Deadly Choices, Offit notes that “anti-vaccine organizations now work hand-in-glove with personal-injury lawyers, many of whom sit on their advisory boards and help them prepare pamphlets that warn of the dangers of vaccines and describe how to collect money.” The genuine benefits of our tort system in improving vaccine safety and deterring wrongdoing receive markedly less attention in his pages.

Mnookin ranges over similar territory, relying on Offit as a primary source. His contribution is to embed the vaccine-autism controversy within a broader story of the anti-scientific tenor of American popular culture. Mnookin is pretty angry, too, as exemplified by some of his chapter titles: “Mark Geier, Witness for Hire,” “A Conspiracy of Dunces,” “Jenny McCarthy’s Mommy Instinct,” “Casualties of a War Built on Lies.”

Mnookin’s most depressing but useful chapter is “Cognitive Biases and Availability Cascades,” in which he describes how people can come to believe things that are plainly untrue. Like an increasing number of policy writers, he draws on the work of cognitive psychologists Daniel Kahneman and Amos Tversky concerning heuristics and biases in human decision-making and perception. Human frailties—our tendency to overstate the likelihood of rare but emotionally salient events, the social amplification of frightening risks, and our proclivity to look for (and find) patterns where they don’t exist—all come into play in the vaccine debate. Who isn’t a bit unnerved at the thought of injecting a healthy infant with a complicated brew of viral proteins and preservatives? What in our experience makes this choice comfortable or obvious, especially when so few of us witness the ravages of whooping cough or measles? A doctor and some big pharmaceutical firm say that a vaccine is safe. Millions of Americans don’t necessarily find this reassuring.

Like-minded ASD parent communities use the Internet to reinforce preexisting fears and biases. Many parents participate in listservs, conferences, and social events where they are bombarded with vivid, terrifying, seemingly believable accounts of alleged vaccine-related harms. The very fact that so many people are discussing the link between vaccines and autism makes it easier for any given individual to believe there is something to it.

These patterns combine with a second problem: “confirmation bias,” whereby people prove adept in finding information that reinforces their own prior beliefs. We prove equally adept at ignoring information that challenges these same beliefs. Add to the mix appealing figures like Andrew Wakefield and Jenny McCarthy, and it’s hardly surprising that herd thinking undermines herd immunity in many communities.

Mnookin notes that these information problems extend beyond vaccines and autism:

Twenty years ago, it took a fair amount of effort to create an information cocoon: In 1987, nearly three-quarters of Americans tuned into a nightly news broadcast from one of the three networks, creating a sort of national common denominator for information about the world. Now that figure has fallen below one-third… . An even more potent force in this regard is the Internet, where it’s easier than not to fall into a wormhole of self-referential and mutually reinforcing links that make it feel like the entire world thinks the way you do. The anonymity and lack of friction inherent in the online world also mean that a small number of committed activists—or even an especially zealous individual—can create the impression that a fringe viewpoint has broad support.

Although the Internet is a big part of the story, Oprah Winfrey’s repeated appearance in these books exemplifies the mainstream media’s harmful role in propagating unfounded, alarmist accounts. A horrifying 1982 television documentary DPT: Vaccine Roulette posited links between vaccination and brain damage in children. Although these claims turned out to be unfounded, Vaccine Roulette helped fuel the modern anti-vaccine movement and promoted costly litigation that led some manufacturers to leave the market.

The media do a generally poor job of reporting supposed controversies in which there is scientific consensus on one side and a committed group of activists on the other. Reporters often pitch the opinions of parents against those of medical experts. This David vs. Goliath frame amplifies the visibility of parents in difficult circumstances who don’t always know what they are talking about, but whose compelling human story commands sympathy and attention—and, incidentally, makes for good television. Mnookin and Offit perform a valuable service when they note that this is no way to educate the public about complex matters.

Still, I closed their books with a nagging sense that something was missing. The crudity of the anti-vaccine movement makes it easy to dismiss populist distrust of medical authorities as mere boobishness, even though it sometimes has legitimate roots. Offit dutifully acknowledges that:

To some extent, pharmaceutical companies have brought this upon themselves… . And it’s not just the unseemliness of promoting lifestyle products that hurts pharmaceutical companies; some marketing practices have clearly evolved from aggressive to unethical. As a consequence, we don’t trust pharmaceutical companies. Nor do we trust the doctors or scientists who work with them.

This, of course, is all too true. Many people died because of Vioxx. Parents rightly feel betrayed by prominent child psychiatrists who pronounced psychotropic drugs as safe without revealing that they had received large payments from pharmaceutical companies. The list goes on. Offit and Mnookin posit a rather stark divide between well-meaning and proficient, albeit politically naïve, scientists, vaccine developers, and clinicians on the one hand and venal exploiters of suffering parents on the other. The divide isn’t always so clear. Things certainly look different within the medical-care system that many families of autistic children routinely see. When a child visibly falls behind in his development, his parents often spend thousands of dollars looking for help and for answers. Too often, they find very poor educational and social services, along with disrespectful, unhelpful, sometimes incompetent medical care.

The vaccine-autism controversy should chasten every participant in this story. Fairly or not, in this day and age many Americans will view physicians and pharmaceutical firms through a lens of conflict of interest and scandal. The medical establishment at every level must maintain a clearer distance from these firms. Offit believes that the American Academy of Pediatrics receives unfair criticism for accepting pharmaceutical support for various good works. He would prefer that consumer advocates stop lobbing incendiary conflict-of-interest charges and operate within established channels of the public-health system. He even refers favorably to epidemiologist Kenneth Rothman’s use of the term “new McCarthyism” to describe excessive distrust of clinicians who work with pharmaceutical firms. Offit has a point, but he’s way out of step with this moment in American politics and culture.

Parents and other caregivers should be chastened too. I speak with some reticence here, since I myself care for an adult with intellectual disabilities. Because of our special experiences and responsibilities, we are granted a platform that creates corresponding responsibilities in discussing delicate and explosive matters. Whether this conversation occurs among caregivers or with the broader public, parents such as Jenny McCarthy who spread unfounded myths do a great disservice.

News media should be more willing to marginalize claims that lack scientific support. Millions of people don’t believe in global warming. These anti-scientific beliefs, however widely and sincerely held, should not be placed on an equal footing with more solidly grounded alternatives. Progressives share blame for this as well. We are quick to recognize the dangers of a war on science when the topic is creationism. We’re slower to see related cultural dangers that hit closer to home, such as when the normally sound progressive instinct to distrust corporate power and embrace parental autonomy lapses into closed-minded rejection of the modern public-health enterprise.

Of course it’s healthy to bear a certain distrust of organized medicine and the biomedical-industrial-research complex. Much good has come from patients’ rights groups rejecting the “doctor knows best” mindset of earlier years. Such groups have agitated for faster drug development and Food and Drug Administration reforms. They have empowered patients to take greater charge of personal health behaviors and medical care decisions. But when a healthy specific distrust bleeds into a generalized anti-scientific worldview, when it leads people to embrace treatments that do not work, or to shirk communal obligations to maintain herd immunity, we need to say “stop.”

The vaccine-autism problem may be ebbing. An investigative reporter discovered that several children in Wakefield’s study were clients of a personal-injury attorney who had secretly paid Wakefield large sums of money. In 2009, a special U.S. vaccine court emphatically rejected claims that MMR vaccines are connected to autism. In 2010, the Lancet retracted Wakefield’s paper. Wakefield has lost his license to practice medicine in England, though he is still honored by segments of the autism community.

His disgrace was long overdue. But it provides little reason for complacency. The lure of magical thinking pervades our culture. It will find a foolish new target soon enough. More important, we in the medical and public-health enterprises give parents too little reason to trust what we say. In failing to show a caring and competent human face, we’ve given too many parents reason to spurn the valuable things we have to offer, sometimes with tragic results.