Autism and vaccines

In my infectious disease class, my professor gave us this article about actress, Jenny McCarthy, and her autistic son. The article is by Sam Wang, a professor of molecular biology and neuroscience at Princeton University. He attempts to explain in this article why people still blame autism on vaccines when there is no scientific evidence to back up that claim.

It is important for people to be critical of the information that they are receiving via the media. As it says in the article, people suffer from "source amnesia." We need to be weary of rumors or other information that doesn't site valid scientific evidence.

Autism myth lives on
Why people continue to blame vaccines, despite evidence to the contrary.
By Sam Wang

As the brother of an autistic person and a brain scientist, I have been hoping that the increased focus on autism in the news would lead to a greater public understanding of this disorder. Instead, I am angry that this coverage is spreading dangerous myths.


My sister, Karen, is autistic. In the 1970s, my parents wondered why she behaved so differently. At the time, a prevalent idea was that an emotionally distant mother could somehow prevent a child from understanding emotions or relating normally to others. Our parents had a simpler idea, that they might have hurt Karen's head during a bath.

Both these ideas are wrong. Autism is a neurological disorder, and its signs appear by the age of 1 or even earlier. It is highly inheritable. In identical twins where one is autistic, the chance that both are autistic is greater than 50-50. Even non-identical twins and siblings are at increased risk. In short, I dodged a genetic bullet. Now I worry about my daughter.


A link that isn't there

Recently, celebrities such as Jenny McCarthy and other activists have taken to the airways to repeat the myth that autism is linked to vaccination. Although peer-reviewed scientific evidence overwhelmingly opposes their views, they have attracted attention. In a recent discussion on Larry King Live, three pediatricians invited to make the case for science were no match for McCarthy's star power. Situations like this could mistakenly persuade parents to leave their children unvaccinated and vulnerable to contagious diseases.


Speculation about a vaccine-autism link began with a 1998 uncontrolled study of a few autistic children. But the conclusions were later retracted. Subsequent speculation focused on the compound thimerosal. But removing it from all routine childhood vaccines in the USA, Denmark, Sweden and Canada has not decreased autism rates.

What are McCarthy's credentials? She is an actress and comedienne — with an autistic son. Her career took on new life after she wrote a best-selling pregnancy guide. Like all parents of autistic children, she wrestled with the question of what caused his disorder. She recalled that her son was vaccinated about the time his symptoms first appeared. Aha! That's it. Here is an example of her reasoning: "I believe that parents' anecdotal information is science-based information."

How we're wired


Although her concept of evidence is flawed, I don't blame her. The error highlights how our brains are wired to think. Like the authors of the 1998 study, she concluded that two events happening around the same time must be linked. They used the principle that coincidence implies a causal link. But there was no coincidence for her son: He was born in 2002, after thimerosal was removed from vaccines.

The problem is compounded by "source amnesia," in which people are prone to remember a statement without recalling where they heard it or whether the source was reliable. Presidential candidate John McCain might have fallen prey to source amnesia when he repeated the vaccine-autism myth last month. Recollection is more likely when the "fact" fits previously held views; parents might already dislike vaccinations based on their kids' reaction to shots. But when it comes to a complex issue such as autism, such errors of reasoning hinder us from distinguishing real causes from coincidences.


Out of sight of the cameras, increased research funding is spurring efforts to find autism's causes. Scientists are vitally interested in possible environmental influences. But the vaccine story is a dry well. Working on it further wastes valuable time and resources. It's time to dig elsewhere.

As I watch my beautiful 10-month-old daughter grow, I wish that preventing autism were as simple as withholding a few injections. But along with my wife, a physician, I understand the vital importance of vaccination, not only for maintaining our baby's health but also protecting our community from infectious diseases. Our daughter's next shots are in two months.


Sam Wang is an associate professor of molecular biology and neuroscience at Princeton University. He is a co-author of Welcome to Your Brain: Why You Lose Your Car Keys But Never Forget How to Drive and Other Puzzles of Everyday Life.
Posted at 12:15 AM/ET, April 16, 2008
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