Health

Beyond the headlines: Link still claimed between thimerosal and autism

Activists stand by their argument despite the fact that science has yet to find proof of the link.

By Kathleen Phalen Tomaselli amednews correspondent — Posted June 19, 2006

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Long before some parents of children with autism backed an April USA Today full-page ad criticizing the Centers for Disease Control and Prevention and charging its experts with a cover-up, the thimerosal war was raging. And, despite a paucity of scientific evidence linking the mercury-based vaccine preservative to autism, such charges continue to find traction. In other words, a growing number of parents doubt the safety and credibility of the very system created to protect the nation's health.

"When you can't argue the data, you go after the people. Hardworking, committed public health servants have been maligned, and it is just shocking," says Martin Myers, MD, associate director for public health policy and education for the University of Texas Medical Branch at Galveston's Sealy Center for Vaccine Development. "This is characterized as a debate. [But] it is not a debate in the scientific realm. This scare has taken on a life of its own, and it's hard to sort out the hysteria."

Caught in a flurry similar to public relations campaigns against conventional public health villains such as big tobacco and asbestos manufacturers, the CDC denounced the ad's allegations. Still, many of the activists adamantly believe their children are mercury poisoned.

"We feel like victims of a terrible crime," says Bobbie Manning, a Buffalo, N.Y., parent of a son with autism and the founder of A-CHAMP -- Advocates for Children's Health Affected by Mercury Poisoning. "It is very similar to what we saw with Vioxx or the tobacco industry. The safety information has been suppressed from the public."

But except for flu vaccine, childhood immunizations are now thimerosal-free, so this heightened unrest leaves some wondering about the continued focus.

"I have been working with autistic kids for 35 years, and there have been concerns about different vaccines since I was 22," says Catherine Lord, PhD, director of the University of Michigan Autism and Communication Disorders Center in Ann Arbor. "It was DPT, MMR, thimerosal and now the flu vaccine. ... Parents are understandably looking for an explanation."

Not all of them see the mercury-poison theory as the answer, adding a new layer of dissonance. "There is so much vitriol," says Kathleen Seidel, the mother of an autistic teen. She started Neurodiversity.com, an online site about autism and related issues. "It's the lure of the jackpot that leads to the exploitation of parents."

Some point to the recent media blitz as part of a bigger anti-vaccine movement, and others view upcoming federal vaccine court deadlines as possible reasons for the stepped-up visibility. But Manning says that's not it. "We are not anti-vaccine. What's driving the interest is so many children affected, and the CDC is not responding." Manning led a small group in lobbying state attorneys general in an effort to get states to join in a lawsuit, similar to tobacco litigation, against the pharmaceutical companies that produced certain vaccines. "These children are mercury-toxic."

Detailing the science

For decades, accusations of vaccine-related maladies have surfaced. So when researchers at Columbia University in New York found a possible association between thimerosal and neurological disorders in early, small-scale studies, anti-vaccine groups took notice. But these results have not been replicated in subsequent research. Even large epidemiological studies in Denmark failed to show a connection. By 2004, the Institute of Medicine proverbially put the issue to bed in its final report.

The American Medical Association has also made clear its support for vaccination. "It's critically important for parents to know that numerous scientific studies show no connection between thimerosal in vaccines and autism," said AMA Trustee Robert M. Wah, MD, in a speech delivered last summer. "We need more research to investigate the actual causes of autism, yet it would be a shame and a disservice to the health of our children if we let vaccines take the blame for this tragic and little-understood disease."

But still, the issue stays in the limelight.

Pediatrics professor Paul Offit, MD, chief of infectious diseases at Children's Hospital in Philadelphia, believes early public education could have quelled flames.

"If we would have simply educated the public at the time. If we had said it's been used safely for 70 years. If we explained that ethyl mercury is structurally different," Dr. Offit says. "But we didn't. Instead, we started to take it out of the vaccines ... and even though we assured people thimerosal was safe; taking it out it made it seem unsafe. People started asking, 'Why are they taking it out if it's perfectly safe?' ... The CDC opened the door, and the anti-vaccine people ran with it."

Dr. Offit blames a confluence of forces. "There are the anti-vaccine people, the parents of kids with autism, the lawmakers and the media. In the current culture there is a belief in cover-ups and conflicts of interest. Thimerosal is out, so why now?" His opinion is clear: "It's the same as the breast-implant litigation. It's a directed, coordinated campaign to educate the jury. This is about lawsuits, about going to court."

Between 2001 and 2006, 5,005 claims have been filed in the federal vaccine court established through the National Vaccine Injury Compensation Program to consider thimerosal-autism related cases. Because litigants must prove injury, the steering committee for the petitioners requested a stay until this fall to develop expert witnesses and the theory for their cases. In addition, thousands of civil actions against manufacturers are under way.

In order to quiet conflict-of-interest charges, the CDC transferred vaccine safety activities from the National Immunization Program to the Immunization Safety Office's Office of the Chief Science Officer, giving thimerosal research priority. Ongoing studies there include:

  • A study of more than 1,000 thimerosal-exposed children evaluated with standardized neuropsychological assessments. Results will be published later this year.
  • A case-control study involving a follow-up of a clinical trial of acellular pertussis vaccine performed in Italy. Two different acellular pertussis vaccines were evaluated -- one with thimerosal, one without.
  • A study exploring autism risk associated with thimerosal exposure by reviewing children from the prenatal period to the first seven months of life.

Some say these and more findings will clear the air.

Mady Hornig, MD, associate professor of epidemiology at Columbia University Mailman School of Public Health in New York, says the complexity of the thimerosal-autism story is part of the problem. She published early studies citing mercury-induced autoimmune outcomes in mice that suggested a genetic basis underlying developmental thimerosal neurotoxicity.

"The literature reports a subset of children with immune disruption. Whether this is solely genetic or triggered by environmental contributors that set the stage for an immune disturbance, we don't know," she says. "A connection is not strongly made on the basis of these few studies alone. We need much more coordinated [research] efforts."

Anti-vaccine and no-mercury groups frequently point to Dr. Hornig's early findings. But there are too many variables that oversimplification does not address, she says. "It will be valuable to have a continued dialogue. I'd like to see the research continue and expand. [Current] studies are not adequate, and more are sorely needed."

Particularly heartening, she says, is the Columbia-led Autism Birth Cohort study in which scientists will follow 100,000 Norwegian babies and their parents for at least five years, beginning during the mother's pregnancy. The goal is to identify biological and environmental factors that could combine to cause autism and other developmental disorders. "We are learning all the time," Dr. Hornig says.

Underimmunization

For public health experts, the potential impact of this movement on vaccination coverage rates is a matter for anxiety. In general, the CDC reported in 2004 that each year 2.1 million children ages 19 months to 35 months are undervaccinated while 17,000 children are unvaccinated. Additionally, nearly three-fourths (71%) of parents who choose not to vaccinate say doctors have little influence over their decisions. Almost half (48%) of these parents expressed a concern about vaccine safety, the CDC's National Immunization Survey found.

"With vaccines, there is no such thing as 100% safe or 100% effective, so we go by the weight of the evidence," says UTMB's Dr. Myers, former director of the Dept. of Health and Human Services National Vaccine Program Office. But changing risk perceptions also have an impact on parents' decisions.

Pediatric medicine is a victim of its own success, says Douglas S. Diekema, MD, MPH, an associate professor of pediatrics at the University of Washington School of Medicine and interim director of the Center for Pediatric Bioethics at Children's Hospital and Medical Center in Seattle. "Fifty years ago people died of measles, and lots of babies were born with malformations from rubella," he says. "When you get that successful, people forget [about these horrors], and that changes the equation for parents. To them, the diseases don't exist anymore."

A recent mumps outbreak, blamed at least in part on underimmunization, is showing how close to the surface these threats remain. The CDC says the U.S. outbreak, which featured the same genotype responsible for more than 70,000 cases in the United Kingdom, continues to spread, with seven states and more than 2,400 cases.

This drama comes up a lot in exam rooms, Dr. Lord says. "We try to get parents to think about what they are doing -- about what's safe and what the risks are. If they aren't going to vaccinate, we ask them how they will protect their child on airplanes, in a big shopping center. We have them think it through."

A few family physicians and pediatricians will not accept patients if vaccinations are refused, a position the American Academy of Pediatrics discourages.

This issue needs to be handled with understanding, Dr. Diekema says. "Parents' concern about the autism issue seems to go up or down with what's in the press, and they don't have a good way of judging opinions. But the reality is most are seeking guidance from their physician. These families are scared, and from what we see, most physicians are trying to have respectful conversations with families coming in with all kinds of [views]."

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ADDITIONAL INFORMATION

Key dates

1986: The National Childhood Vaccine Injury Act establishes the National Vaccine Injury Compensation Program, including a special court to consider vaccine-related claims.

1997: The Food and Drug Modernization Act requires the Food and Drug Administration to compile a listing of mercury in food and drugs.

1999: As a precaution, vaccine manufacturers begin removing thimerosal from childhood vaccines.

2000: Thimerosal-free vaccines against hepatitis B and bacterial meningitis are widely available; organizations such as Safe Minds take form to press grassroots educational efforts regarding the alleged connection between thimerosal and autism.

2001: An Institute of Medicine Safety Review Committee concludes that no clinical or experimental evidence supports the thimerosal neurodevelopmental disorder theory.

2002: In a University of Rochester (New York) study published in the Lancet, researchers conclude that mercury levels in the blood of infants receiving vaccines with thimerosal are below concentrations potentially associated with toxic effects.

2002: Thimerosal/autism claims proceedings begin.

2003: The last of the thimerosal-preserved vaccines for children (except flu) come off shelves.

2003: Landmark Danish study discounts a link between thimerosal in vaccines and neurological disorders.

2004: The American Academy of Pediatrics, American Academy of Family Physicians, the CDC vaccination advisory committee, and the Public Health Service maintain there is no convincing evidence of harm.

2004: An Institute of Medicine final report, "Vaccines and Autism," concludes that the body of epidemiological evidence rejects a relationship between thimerosal-containing vaccines and autism.

2005: Vaccine Safety Datalink is established by the CDC to study possible safety problems.

2006: Anti-vaccine and anti-thimerosal groups sponsor USA Today ad accusing the CDC of covering up an autism epidemic; the CDC reports that at least 300,000 school-aged children had autism in 2003-04.

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External links

National Network for Immunization Information (link)

National Influenza Vaccine Summit, co-sponsored by the American Medical Association and the Centers for Disease Control and Prevention (link)

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