Ever since Robert F. Kennedy Jr. alleged a government cover-up in his controversial Salon article "Deadly Immunity" last June, and New York Times writer David Kirby alleged a connection between autism and childhood vaccination in his book Evidence of Harm, the controversy over whether thimerosal causes autism has returned to both talk radio, news stories and the nation's editorial pages.
Seven states, including California, have acted to virtually ban thimerosal. Legislation in Tennessee would have banned kids receiving flu shots because of fears of thimerosal. Lawmakers in 20 states are pursuing restrictions, despite the protests of American Academy of Pediatrics and opposition by the Food and Drug Administration and most health experts.
Why all the fear and panic in the face of health professionals saying, don't worry? Perhaps, because this seven-year-old junk science is different. It is one without the "usual suspects."
With most junk science alarms there is usually some purveyor of corrupted science who is trying to peddle his wares under the banner of real science. Sometimes it's a "public interest group" whose only real interest is scaring people into conforming to someone else's agenda. Often it's some government agency eager to further its own power through harnessing the agency of the state to shape people's lives through scientific misinformation.
In the matter of thimerosal, a mercury-based preservative used in vaccines, and whether it causes childhood autism, that is not the case. There are, to be sure, the usual trial lawyers hovering in the background, plus a headline seeking crusader, in this case one with the Kennedy name. And several church groups have launched campaigns to rid all vaccines, including the flu vaccines, of thimerosal. But for the most part, the campaign to convince government and the public that vaccinating young children leads to autism is the product of hundreds of heartsick parents whose children have autism.
The debate and worries about vaccines and autism has simmered around the edges of the scientific community for some time. But it hit the front page in 1998 when one of the world's most prestigious medical journals, The Lancet, published an article, replete with obscure terms -- "Ileal-Lymphoid-Nodular Hyperplasia, Non-specific Colitis, and Pervasive Developmental Disorder in Children" -- by a young British specialist in pediatric gastroenterology, Dr. Andrew Wakefield. Wakefield had looked at a group of young children who had suddenly lost a range of skills, including language abilities, and who suffered from abdominal pain and diarrhea. He suggested that the source of the problem might be the childhood vaccine MMR (Measles-mumps-rubella).
Wakefield's study, which was quickly picked up by the press, set off a panic, first in the UK and latter in North America. Some researchers and reporters claimed that there was a silent autism epidemic, with large, but hidden increases in the number of autistic children worldwide due to vaccinations containing the mercury preservative. Additionally, several parent groups, such as Safe Minds and Moms Against Mercury, launched national campaigns claiming the pharmaceutical industry, the scientific community and governments had been systematically suppressing the truth about the risks of thimerosal.
The stories led worried parents to believe that childhood immunizations were likely to cause autism. A 2000 survey in Pediatrics reported that 25% of parents had serious concerns about the vaccines given to their children. And significant numbers refused to vaccinate their children, with predictably unfortunate consequences.
In 2000, Ireland, reported 1,603 cases of measles -- 10 times more than the year before. Another surge to 572 cases occurred in 2003. By comparison, the US, with a population 75 times greater, had 86 measles cases in 2000 and 116 in 2003. In Colorado and Oregon where parents concerned about autism are allowed to decline immunization for their children, diseases like whooping cough are already returning. For instance, in 2004, Colorado, a state with just under a 70th of the population, had more than a 10th of the total number of cases of pertussis -- whooping cough -- 1,210 cases.
Autism is a terrible diagnosis for any parent to receive, but however much one sympathizes with parents and their children, the question still is: What is the scientific evidence that thimerosal in vaccines causes autism?
In 2004, the U.S. Institute of Medicine, which had been commissioned by the U.S. government to examine the epidemiological data, along with the idea of whether a connection between thimerosal and vaccines was biologically plausible, concluded that the majority of the evidence "favors rejection of a causal relationship between thimerosal and autism." The evidence that the Institute relied upon consisted of five major epidemiological studies from the US, the UK and Sweden, all completed since 2001, which looked at the links between various vaccines containing thimerosal and autism, and 14 other epidemiological studies that focused on the MMR vaccine and autism.
Two of these studies, both published in 2003, are particularly important since they highlight how weak the case against thimerosal is. The first (Stehr-Green et al "Autism and Thimerosal Containing Vaccines: lack of Consistent Evidence for an Association," AJPM, 2003) compared thimerosal exposure and autism rates in children in Denmark, Sweden and California.
In each jurisdiction, the study found autism rates started to increase from 1985. In Sweden and Denmark the increase continued into the 1990s even though thimerosal was eliminated from vaccines in 1992. Indeed, in Denmark the increases were substantial. Where before 1992 there were about 10 new autism cases per year, by 2000, eight years after all thimerosal had been removed from vaccines, there were 181 cases a year. Similarly, in Sweden, autism rates continued to increase even after thimerosal was removed from vaccines. Because of this lack of a consistent connection between thimerosal and autism, the researchers concluded that the hypothesis that thimerosal caused autism was inconsistent with the scientific evidence.
The second study appeared in the Journal of the American Medical Association (Hviid et al., "Association between Thimerosal-Containing Vaccine and Autism," October, 2003), and its results were even more dramatic. Led by Anders Hviid of the Danish Epidemiology Science Center, the researchers examined the medical histories of all children who were born in Denmark from 1990-1996, almost 500,000 children. Thimerosal vaccines had been eliminated in Denmark in mid-1992, so the study was able to examine two groups of children, those who received vaccines with thimerosal from 1990-1992 and those from 1993 onward who did not.
The children who had received vaccines with thimerosal had a non-statistically significant relative risk for autism of 0.85, compared with the thimerosal-free group, which meant that they were 15% less likely to get autism. There was also no dose-response link -- where risk increases with exposure level -- leading the research group to conclude that "the results do not support a causal relationship between childhood vaccination with thimerosal-containing vaccines and development of autistic-spectrum disorders."
More recent studies, including one in Pediatrics (September 2004) support these conclusions. The Pediatrics article looked at 12 different studies on thimerosal vaccines and autism published from 1966-2004 and concluded: "Studies do no demonstrate a link between thimerosal-containing vaccines and autistic spectrum disorders." Equally interesting, the authors looked at the blood mercury levels found in children after receiving vaccinations and concluded that they did not fall within the toxic range.
Moreover, autism researchers consistently caution that autism is not a single condition but a highly complex group of developmental disorders. There is no agreement on the rate of autism, though two recent reviews have placed it at one case for every 1,000 children. Indeed, it is not even clear whether autism is increasing or whether it is simply being more accurately diagnosed.
Meanwhile a new study released in May 2005 in the American Journal of Epidemiology found the causes of autism in a variety of factors unrelated to thimerosal. According to researchers from Denmark, the CDC and Johns Hopkins, "[H]eredity and early fetal development play a causal role in autism." They suggest that autism might be associated with a parental psychiatric history of schizophrenia; affective disorders, including depression and bipolar disorder; breech presentation of the baby, and early birth.
None of this science can lessen the tragedy of autism. But perhaps it can provide some measure of comfort to all parents by reminding them both that childhood vaccinations are crucially important for the health of their children and reassuring them that the vaccination system is safe.
John Luik is writing a book on health policy.