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Congressional Autism Hearings Continue:
No Evidence MMR Vaccine Causes Disorder
Journal of the American Medical Assn - Vol. 285 No. 20, May 23/30, 2001
Washington - Congressman Dan Burton (R, Ind) refuses to take "no" for an answer. At his latest congressional hearing looking into possible links between autism and childhood vaccines, Burton railed against panels of assembled scientists. At one point, he slammed down a recent Institute of Medicine (IOM) report which concluded there was no evidence that the measles, mumps, and rubella vaccine (MMR) leads to autism and shouted, red-faced, "You don't know there's no link, do you? Do you?"
Marie McCormick, MD, professor at the Harvard School of Public Health and chair of the IOM committee that proffered the report, quietly replied, "I know it's not causing most of the cases of autism. The level of analysis we were able to do does not rule out rare occurrences."
Those possible rare occurrences, which even the best epidemiology is not equipped to detect, is where science becomes personal for Burton. His grandson, Christian, was diagnosed with regressive autism subtype in which a normally developing child suddenly withdraw shortly after receiving nine vaccines in one day. Burton clearly believes the injections caused the disorder; he repeatedly invoked his grandson's case. And as chair of the House Committee on Government Reform, whose purview ranges across every federal agency, he has the power to push the issue.
In late April, he called another in a continuing series of hearings, and the IOM committee sped through its review process to publish in time for the session. Earlier pressure from the congressman had led the IOM to select a panel of experts with no financial ties to the vaccine industry. The resulting group has no vaccine experts, a fact that led one hearing witness, Columbia University's Michael Gershon, MD, to later say, "This is the most peculiar panel ever constituted by the IOM."
And yet Burton grilled McCormick and other IOM representatives about the financial interests of the committee members and the report's peer reviewers, who were subject to less stringent disclosure requirements. He threatened to subpoena financial records from all of the reviewers and questioned whether the universities employing them had ever received money from the pharmaceutical industry.
"If we excluded everyone who works for a university that receives grants from the drug industry, there would be no one left" to serve as reviewer, answered Susanne Stoiber, the IOM's executive director.
Burton then questioned how much influence the reviewers wielded, to which McCormick responded, "None of our recommendations or conclusions were changed after peer review."
One of the hearing's witnesses took umbrage at the congressman's tactics. "Congressman Burton is alleging that the IOM was in conspiracy with the vaccine manufacturers," said Gershon, who is chair of the Department of Anatomy and Cell Biology at Columbia, in a posthearing phone interview. "[Burton] doesn't believe in coincidences, but unlucky coincidences happen all the time. It's time for congressman Burton to realize it's time to move on."
Concerns about the MMR vaccine and autism first surfaced in Great Britain in 1998, when gastroenterologist Andrew Wakefield, MD, reported on 12 children with developmental disorders (nine with autism) who had gastrointestinal disturbances similar to irritable bowel syndrome (Lancet. 1998;351:637-641). Wakefield's team decided to look for measles virus in the intestines of such children, and began to formulate theories about a possible link between MMR vaccine and a subtype of autism that includes bowel symptoms.
At the same time, anecdotal reports from parents began to surface. Four of these parents, who are physicians, were called to testify at the US congressional hearing. They recounted similar experiences: their children received vaccinations, followed by behavioral changes, bowel disturbances, and a diagnosis of autism. Combined with parental reports, Wakefield's publication triggered several epidemiological studies, culminating in the IOM's review.
To date, none of the epidemiological evidence suggests that MMR vaccination leads to autism. "There's no evidence that the onset of [autistic] symptoms is more likely to happen right after the vaccine," said Elizabeth Miller, PhD, of the British Public Health Laboratory Service. She added that, among 500 children with regressive autism and bowel symptoms in the North Thames region of England, roughly equal proportions received the vaccine before and after parents became concerned about autistic symptoms. An equal proportion had never received MMR vaccine. Her conclusions were first published 2 years ago (Lancet. 1999;353:2026-2029); a follow-up report, in press at the journal Vaccine, provides evidence, said Miller, that MMR vaccine does not increase the risk for autism at any time after vaccination.
Reports from the United States offer buttressing results. A recent study from California shows that the number of children with autism in that state's mental health services system increased rapidly between 1980 and 1994, while the proportion of children immunized with MMR remained relatively stable (JAMA. 2001;285:1183-1185). The authors noted that if the vaccine were causing autism, the trends should be parallel. Another review, from the American Academy of Pediatrics published in the May issue of Pediatrics, reached conclusions similar to the IOM's.
At the Burton hearing, Wakefield countered that more clinical investigation is needed before epidemiology can offer definitive answers. He said data presented at a recent autism conference at Cold Spring Harbor Laboratory in New York show measles virus, in one cohort, in the intestines of 93% of children with autism and in only 11% of controls. He called for other clinicians to replicate his work; so far, none have. Wakefield also said his studies have been misinterpreted by Miller and the IOM. "We're not saying it [MMR vaccine] is the cause [of autism], but we are saying, 'What's going on?'" Wakefield proposed pursuing several new avenues of research, including the possibility that children with autism have a strong family history of autoimmune disorders; that preexisting allergies contribute to susceptibility; and that receiving several vaccinations concurrently creates a higher risk than receiving them separately.
Soon after Wakefield's testimony, Columbia's Gershon, a self-described "gut expert," explained the biological implausibility of an MMR-autism connection, which he said would require "three miracles." First, after the virus took up residence in the gut (a controversial proposition), it would have to create a toxin that could leak out of the intestines; then it would have to bypass the liver; and finally it would need to breach the blood-brain barrier.
But one of the parent-physicians who testified, James Bradstreet, MD, of the International Autism Research Center, Palm Bay, Fla, speculated that another process, autoimmunity, was at work. He suggested that researchers explore interactions between various vaccines, with a keen eye on autoimmune responses. "A number of environmental factors can skew kids toward autoimmune, so by the time they get to 15 months, for some of them it [the MMR vaccine] is just too much," said Bradstreet. "It's not just the MMR vaccine itself."
Until scientists explore these possibilities, the fact remains that every large study of the MMR-autism connection refutes a causal link. But none of them offer 100% reassurance. "No epidemiology could prove that the vaccine never causes autism," said Britain's Miller. "Proof of a negative is impossible."
Increasing Prevalence, Increasing Research
With no known cause and few useful treatments, autism remains an enigma. And by many accounts, it is becoming more common. Some witnesses at a recent congressional hearing said that recent data show an epidemic is afoot. Others took a more cautious view. "We don't know if these higher rates are due to different diagnostic criteria, better recognition and reporting, study phenomena, or if they represent a true increase in rates of autism," said Coleen Boyle, PhD, of the Centers for Disease Control and Prevention (CDC).
Boyle's uncertainty stems from the lack of incidence data on autism. While reports of growing prevalence are common including a 373% increase in California from 1980 to 1994age-specific incidence rates are needed to establish the existence of an epidemic, said epidemiologist Walter Spitzer, MD, MPH, of McGill University in Montreal. However, incidence data are beginning to trickle in. A recent report from Great Britain (BMJ. 2001;322:460-463), for instance, shows a sevenfold increase in age-adjusted incidence from 1988 to 1993.
Along with this trend comes increasing research dollars. The National Institutes of Health (NIH) reports spending $22 million on the disorder in 1997 and $52 million in 2000. The NIH hopes to increase the breadth of its autism research program substantially over the next few years. At the CDC, a new Center on Birth Defects and Developmental Disabilities is gearing up for better monitoring of autism rates. Elsewhere, at the University of California – Davis School of Medicine, a new institute called MIND (Medical Investigation of Neuro-developmental Disorders) is breaking ground on a $34-million building and an ambitious agenda to trace the roots of autism and find diagnostic markers.
It appears that all of these efforts will enjoy congressional support. In February, 113 members announced the Congressional Autism Coalition, which vowed to increase funding for research on autism.
Next Up for Scrutiny: Mercury-Containing Vaccines
With questions about the MMR vaccine's link to autism largely resolved, the Institute of Medicine's specially convened Immunization Safety Review Committee began tackling another big question: whether vaccines containing the mercury-based preservative thimerosal are responsible for increasing rates of autism.
In 1999, the US Food and Drug Administration (FDA), acting on recommendations from the American Academy of Pediatrics and others, began working with vaccine manufacturers to eliminate thimerosal from vaccines. "This was a precaution," said Karen Midthun, MD, director of the FDA's Office of Vaccine Research and Review, during intense questioning from Dan Burton (R, Ind) during the congressional hearing on vaccines. Midthun said that some vaccines containing thimerosal, including diphtheria, tetanus, and pertussis (DTaP) vaccine, remain in circulation. She added that the manufacturer of DTaP vaccine would be releasing two more lots of thimerosal-containing vaccines in the near future.
"Why haven't you recalled the existing vaccines?" Burton asked.
Midthun answered that public health laws allow a recall only if there is "a recognized public health threat."
Burton pressed Midthun to ask the manufacturer not to release any more of the thimerosal-containing DTaP vaccine. "There's no latitude in the public health laws," responded Midthun.
"You ought to get it out of there," said Burton. "The pressure you're feeling now is going to be magnified many times."
Meanwhile, results from one important study are due soon. Researchers at the University of Rochester School of Medicine and Dentistry and the National Navy Medical Center, Bethesda, Md, are comparing mercury levels in hair, blood, and urine samples from children with autism with samples from controls. The IOM report on thimerosal is expected later this year.
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