[Archived text from Brainlink: A project of the Center for Mental Health and Media, supported by a grant from the National Institute on Drug Abuse. By Cheryl K. Olson, Sc.D.]
Could the brain’s need to find patterns help explain the persistent belief that vaccines can trigger autism?
When we look back at the ravages of diseases like smallpox and polio, it’s no wonder that vaccines have been hailed as being among the most powerful tools ever developed in medicine.
So why are so many people convinced that another vaccine—the one for measles, mumps, and rubella, or MMR—is to blame for an apparent increase in autism, a brain disorder? And why are they still convinced, even after a federal court ruled in early 2009 that the supposed link was, in essence, nonsense?
The answer may lie in the way our brains process information.
History of the claim
In 1998, a study was published by a group of British doctors, suggesting a link between autism and gut problems. It was based on the cases of 12 children who had developmental disorders (including autism). The parents of eight of those children said they first noticed problems a few days after their children were vaccinated. Later, the same researchers reported that traces of measles virus had been found in the guts of 24 out of 25 autistic children. The doctors suggested that the MMR vaccine had not been properly tested for safety, and that it might be linked to autism.
Using statistical analyses of very large groups of children—what are known as epidemiological studies—other researchers looked for a link between autism and the MMR vaccine. Again and again, studies from Sweden to Japan have shown that the alleged relationship just doesn’t hold up. Also, serious problems were found with the British studies that set off the scare. But the results had received international publicity. The idea of the vaccine-autism link took off, and persists.
Feb. 2010 update: the 1998 British study was retracted by the medical journal The Lancet.
Picking out patterns
The MMR vaccine is given around the same time that the first symptoms of autism usually appear. A toddler with autism may have started talking and interacting normally, only to regress, withdraw, and lose her words. Desperate parents try to make sense of what’s happened. They find that, although scientists have identified some risk factors for autism, the cause of autism is still uncertain. Some parents conclude that because their child seemed fine before the vaccination and became sick afterwards, it must be because of the vaccine.
The human brain is very good at picking out patterns. So good, in fact, that it sometimes sees patterns that aren’t really there. For example, think about all those ancient astronomers who drew maps of the stars that showed archers and rams and giant scales.
It turns out that when we lack control over a situation—such as when our child is sick, and we don’t know why—the need to find a pattern goes into overdrive. An unexpected event, even a happy accident, prods us to identify a cause and regain a sense of control. (This is one factor that drives superstitious behaviors, and conspiracy theories.)
Researchers at the University of Texas at Austin tested this idea in a series of experiments. They found that when people feel a lack of control, they are more likely to see images in random static, and to perceive nonexistent stock market trends. In every case, lack of control led people to seek some kind of predictability by creating patterns out of “noise.”
In the same way, parents (and even some experts) may pay too much attention to the small number of cases in which, simply by coincidence, the symptoms of autism appear soon after the vaccination, and ignore the many cases when that isn’t true. Our brains look for a pattern and think they find it…even when it doesn’t exist.
In a way, vaccines are a victim of their own success. Because we don’t see the diseases they prevent, we forget the suffering, lingering problems and deaths they caused. Instead, we focus on the potential for harm from vaccine side effects.
Another factor at work is what researchers call “confirmation bias.” Once we think we’ve got a reasonable explanation for a problem, we look for evidence to support that conclusion. And, we downplay any evidence that undermines it.
The “vaccine court ” decision in a nutshell
The National Vaccine Injury Compensation Program (VICP) was created out of concern that the fear of lawsuits would lead drug makers to stop making vaccines for childhood diseases. Now, if someone believes a child was injured by a vaccine, they file a petition for compensation with the U.S. Court of Federal Claims.
The petitions of three families were heard as tests of the idea that vaccines could cause autism. The results of these test cases would then guide future rulings.
Three basic conditions had to be met to allow the cases to go forward:
1. Was there a plausible science-based theory about how the vaccine might have caused the injury?
(The theory was that a type of autism might be caused by the MMR vaccine, by a preservative called thimerosal formerly used in some other childhood vaccines, or by some combination of the two. In particular, it was thought that exposure to thimerosal in earlier shots could damage a child’s immune system. This damage might then allow the weakened measles virus from the MMR vaccine to linger and harm the child’s gut and brain.)
2. Was there a logical sequence of cause and effect between the vaccination and the child’s illness?
3. Was there evidence that the vaccine and the illness happened close enough together in time that one could have caused the other?
The court’s Special Masters heard or read testimonies from many experts, and reviewed hundreds of medical and scientific articles. They had to decide, Did the bulk of the evidence support the vaccine-autism link, or not? Or, might it show that the child’s autism was caused by something else? Eventually, the court found that evidence did not support the first two conditions above.
“Because the linchpin of petitioners’ theory, the finding of persistent measles virus in the biopsied tissue taken from the gastrointestinal lining of autistic children, is glaringly unreliable, the basis for Dr. Corbier’s opinion that the MMR vaccine was causally related to [the child’s] autism and his gastrointestinal symptoms is critically flawed and scientifically untenable. Petitioners have failed to prove that their theory of vaccine-related causation is biologically plausible…. Nor have petitioners demonstrated that the unsupported links of their proposed causal chain cohere to establish a logical sequence of cause and effect as required…. Having failed to satisfy their evidentiary burden, petitioners cannot prevail on their vaccine claim. Accordingly, the undersigned need not reach or consider any alternative theories of causation.” (p. 199)