Other than UFOs, there may be no hotter topic for conspiracy theorists than the claim that childhood vaccines cause autism. There are more than 150 Web sites devoted to fingering various vaccines for the severe neurological disorder. Many blame a mercury-based preservative called thimerosal, used in some vaccines, while others blame the measles-mumps-rubella vaccine, although it never used thimerosal. The only commonality is that autism appears shortly after the period during which childhood vaccinations are given. The theorists take this "post hoc" fallacy, add suggestive quotations (often taken out of context), toss in a few "experts" and claim cover-up – so far, unconvincingly.

Journalist David Kirby got the formula down pat in Evidence of Harm, a recent book. Now so has Robert F. Kennedy Jr., a senior attorney for the Natural Resources Defense Counsel (the group that brought us the Alar scare). His "Deadly Immunity," an article co-published by Rolling Stone and Salon, has won praise from both left and right. The American Prospect hailed it as a "blockbuster piece." Joe Scarborough, on his TV show, said that "there’s no doubt in my mind that thimerosal causes, in my opinion, autism." In the article Mr. Kennedy claims that a metabolite product of thimerosal, ethyl mercury, is "a potent neurotoxin" injected into children with vaccines.

But Mr. Kennedy isn’t to be relied upon for facts. He told Mr. Scarborough in a June 21 interview: "We are injecting our children with 400 times the amount of mercury that FDA or EPA considers safe." Yet four days earlier this correction to his piece appeared: "The article also misstated the level of [mercury that infants have received]." It was "40 percent, not 187 times, greater than the EPA’s limit for daily exposure to methyl mercury." Mr. Kennedy not only ignored this correction on Mr. Scarborough’s show; he overstated it even further. More important, the mercury associated with thimerosal isn’t methyl mercury (the bad actor that accumulates in fish) but ethyl mercury, which, according to the National Institutes of Health, appears to be more benign.

Throughout Mr. Kennedy’s article he confuses the two mercury forms. More important, he avoids the mass of refereed epidemiological studies and reviews of those studies except for his swift dismissal of the Institute of Medicine 214-page report from May 2004, which concluded: "The evidence favors rejection of a causal relationship between thimerosal-containing vaccines and autism."

The most recent review of the published work appeared in the September 2004 issue of Pediatrics. It concluded that "studies do not demonstrate a link between thimerosal-containing vaccines and Autistic Spectrum Disorders." It also said the way the body absorbs and disposes of ethyl mercury "make such an association less likely" and epidemiological studies "that support a link demonstrated significant design flaws that invalidate their conclusions."

Instead, Mr. Kennedy quotes from vaccine conspirators like Boyd Haley, "one of the world’s authorities on mercury toxicity." Actually, Mr. Haley has co-authored, since 1993, a total of five mercury-related publications listed on the medical data base Medline – not exactly what you’d expect from a world authority. By contrast, Frank DeStefano, an epidemiologist at the CDC who does not believe that vaccines cause autism, has co-authored 49 vaccine papers.

Mr. Kennedy also relies on publications from the father-son team of Mark and David Geier, who make their living as expert witnesses and consultants for lawyers making claims under the National Vaccine Injury Compensation Program. Yet health professionals dismiss their work, with the American Academy of Pediatrics condemning Geier publications for containing "numerous conceptual and scientific flaws, omissions of fact, inaccuracies, and misstatements."

The most arresting part of Mr. Kennedy’s article, though, was his allegation of a conspiracy. In June 2000, the Centers for Disease Control and Prevention held a conference at the Simpsonwood Conference Center in Norcross, Ga. The doctors and scientists gathered there discussed a preliminary study that indeed found a statistically significant link between thimerosal-preserved childhood vaccines and autism. From material obtained via the Freedom of Information Act, Mr. Kennedy selected quotes that seemed to leave no doubt that the meeting’s purpose, ultimately, was to (as Mr. Kennedy puts it) "whitewash the risks of thimerosal, ordering researchers to ’rule out’ the chemical’s link to autism."

Tom Verstraeten, a CDC epidemiologist who was at the conference and played a part in the study, explained in a letter to the April 2004 Pediatrics that the Simpsonwood research was in fact "perceived at first as a positive study" – meaning a study that showed a harmful correlation. He himself was quite impressed by the findings. But it "was foreseen from the very start that any positive outcome would lead to a second phase" because "the validity of the first-phase results needed urgent validation in view of the large potential public health impact," he wrote. That seems logical unless you believe that thimerosal is inherently evil, as Mr. Kennedy perhaps does. He thinks the CDC should have taken "immediate steps to alert the public and rid the vaccine supply of thimerosal."

And what did further research show? The second-phase study, the results of which appeared in the November 2003 issue of Pediatrics, concluded: "We found no consistent significant associations between thimerosal-containing vaccines and neurodevelopmental outcomes." Nevertheless, it declared that more research was needed. Mr. Kennedy’s explanation for the shift in outcomes is that Mr. Verstraeten, who oversaw the second-phase research, "had gone to work for [vaccine maker] GlaxoSmithKline and reworked his data to bury the link between thimerosal and autism."

Aha! But this is pure surmise, assuming a level of corporate skullduggery that beggars belief. In any case, consider: If you were part of a government-Big Pharma conspiracy, would you call for more research, as Mr. Verstraeten did? Dr. DeStefano, the epidemiologist at the CDC, has noted that, in addition to extensive CDC internal review, the second-phase research was reviewed "by external experts, by an Institute of Medicine committee, and by peer reviewers for Pediatrics."

Dr. DeStefano explained something else. Mr. Kennedy had claimed that "to thwart the Freedom of Information Act," the government "handed its giant database of vaccine records over to a private company, declaring it off-limits to researchers." But this practice, Dr. DeStefano noted, was required by federal regulations to protect the privacy of autistic children and their parents. It still allowed access by external researchers but not to any Joe Blow with a FOIA application.

Repeatedly Mr. Kennedy’s conspiracy claims vanish like a vampire exposed to sunlight. Which might be amusing were it not so serious. The conspiracy-mongers have scared parents into not protecting their children. "Sadly, as exemptions proliferate, disease ’hot spots’ are cropping up across the United States," observed an article in the Winter 2004 University of Michigan Journal of Law Reform. "Outbreaks of measles, whooping cough, mumps, rubella and diphtheria are reoccurring, costing hundreds of lives and hospitalizing thousands more."

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Read Michael Fumento’s other work on disease and on pharmaceuticals.