Debate Grows On Vaccine-Autism Link
Stakes are high as panel reviews risk from mercuryFeb 8, 2004 | Boston Globe The new vaccines kept coming, each containing a tiny amount of mercury as a preservative. For nearly a decade, until regulators realized the problem in 1999, children who received all the recommended vaccinations could have absorbed an elevated amount of the toxin by the time they were 6 months old.
"I feel badly that I didn't pick it up," acknowledged an adviser to the National Immunization Program, Dr. Neal Halsey of Johns Hopkins University, at a hearing in Cambridge three years ago.
The preservative, called thimerosal, is used only in trace amounts or not at all in today's US vaccines, but the debate over the human cost of that public health miscalculation is growing. Tomorrow, a panel of the Institute of Medicine will hear new evidence on whether mercury-containing vaccines could explain the apparent increase in autism, a neurological disorder whose victims have difficulty interacting with others or even with talking, and often rely on ritual behavior to cope.
By some estimates, the number of US autism cases has risen tenfold in the past 30 years, although it is unclear how much of the increase reflects greater awareness of the disease rather than a true rise. Many public health officials say the amount of mercury was too small to do much harm, but parents of autistic children say their concerns are not getting a fair hearing because federal health agencies, along with vaccine manufacturers, manipulate studies to play down the role of vaccines in neurological problems.
"I just want to figure out what happened to my kid," said Mark Blaxill of Cambridge, whose 8-year-old daughter was diagnosed with autism shortly after she received childhood immunizations.
The anticipated hearing in Washington marks the second time that the institute, an independent science adviser to the government, has tackled the emotional and politically charged issue. In 2001, it concluded that it is "biologically plausible" that mercury, used since the 1930s to keep vaccines fresh, causes autism. The institute's Immunization Safety Review Committee found insufficient evidence to substantiate the claim but recommended that mercury be phased out of vaccines for children as a precaution.
Since then, advocacy groups have zeroed in on changes in the vaccine program beginning in the late 1980s as a possible cause of the apparent increase in autism cases. In that period, a broad effort to increase vaccination rates raised the number of children getting thimerosal-containing vaccines, and new vaccines for hepatitis B and a form of bacterial meningitis were added. The US Food and Drug Administration found that an infant would receive more mercury from the shots than the federal safety standard for mercury in the environment, although mercury in vaccines takes a different chemical form.
But studies in the past three years have reached conflicting conclusions about whether any harm was done. The federal Centers for Disease Control and Prevention has found no consistent link, but other specialists, such as Richard Deth of Northeastern University, have found in laboratory experiments that the form of mercury in vaccines can disrupt chemicals that are key to the developing brain.
The stakes in the vaccine review, expected to be made public by May, are enormous, both for the parents of autistic children and for the US childhood immunization program. Already, 3,500 families of autism patients have applied to the National Vaccine Injury Compensation Program, a federal fund that pays hundreds of thousands of dollars for proven vaccine injuries. Hundreds of other families of autism sufferers have sued the government and vaccine makers directly. But "no one has been compensated one penny yet alleging that mercury in vaccines causes autism," said Jack Hamilton, a lawyer in Melbourne, Fla., who represents more than 50 claims before the compensation program.
More broadly, researchers say the thimerosal controversy has contributed to growing anxieties about children's scheduled shots, and they fear a drop in immunization rates even though today's vaccines, collectively, contain 60 times less thimerosal than the 1990s vaccines. A new University of Michigan survey found that 93 percent of pediatricians had encountered at least one parent who refused vaccines for his or her child in the past year.
"We can do tremendously more harm if we in fact create an environment where children don't get vaccines and we begin to have outbreaks of vaccine-preventable illnesses," said Dr. Gary Freed, director of the Child Health Evaluation and Research Unit at the University of Michigan and author of the study.
Critics say the CDC itself may have undermined confidence in vaccine safety with a study published last November that found no consistent link between mercury in vaccines and autism. The study, based on a review of records from three health maintenance organizations, found only scattered evidence of an increased risk of tics and speech delays but not autism for children exposed to thimerosal. The study called for further investigation.
But SafeMinds, an advocacy group, obtained the transcript of a meeting in July 2000 in which study authors and advisers discussed preliminary findings that indicated the risk of autism was 2 1/2 times greater among children who received the highest levels of thimerosal compared with those who received none. "I do not want [my] grandson to get a thimerosal-containing vaccine until we know better what is going on," said Richard Johnston, a pediatrics professor at the University of Colorado, according to the transcript.
The version of the study published in the journal Pediatrics last year found no such link, in part because the researchers obtained new data on children from Harvard Pilgrim health plan that diluted the original findings.
US Representative Dave Weldon of Florida, one of the few doctors serving in Congress, is pressing the CDC to give outside researchers access to the study data and calling for an independent review. "There may have been a selective use of the data to make the associations in the earliest study disappear," he wrote to CDC director Julie Gerberding.
CDC spokesman Von Roebuck declined to respond publicly to Weldon's charge, although the researchers have said they collected the Harvard Pilgrim data to broaden their analysis. And Roebuck defended the CDC's objectivity in the vaccine debate: "We're really trying to take a look at the science and understand it."