Do vaccines cause autism?

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An Iraqi child is vaccinated by a nurse during an immunization program in Baghdad. See more vaccine pictures.

Your health is one of those things you don't think about too much unless something's wrong. People who are sick think about their health a lot. People who have sick loved ones think about health a lot, too. And for the past several years, some people whose loved ones have autism have thought about vaccines a lot.

Vaccines aren't exactly a modern invention. After realizing that people who survived smallpox never got it again, people started inoculating themselves around 200 B.C., hoping that a little bit of exposure in the present would save them from a devastating illness in the future [source: National Museum of American History]. Unfortunately, primitive methods, which used a live virus from infected material, could result in the patient getting a full-blown case of the disease.

The big idea behind modern vaccines is this: You introduce a weakened (attenuated) or dead form of a disease into your body so that your immune system learns how to make the antibodies that fight it. That way, if you ever run into the real thing, your body is prepared to clobber it.

And vaccines work. They may be the single greatest medical discovery in history. Your body can take care of some sicknesses, but other diseases race through your system like wildfire and destroy your body. Smallpox, the Great Influenza, the Black Death -- these epidemics devastated the world's populations, sickening and killing millions of people.

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��Most people start getting vaccinated as infants against a veritable "lions, tigers and bears, oh my" list of diseases: Hepatitis B, rotavirus, diphtheria, tetanus, pertussis, Hib, polio, measles, mumps. If someone asked you to describe the symptoms of all of those diseases, you probably wouldn't be able to unless you're in the medical profession. That's because we rarely see these diseases anymore, because we're protected by vaccines.

�But there's another disorder we're seeing more and more of: autism. Or rather, we're seeing more of a group of conditions, known as autism spectrum disorders (ASDs). Like any disorder, autism is tough. It's especially tough on caretakers. Some kids with ASDs like Asperger's are able to function in society, although with difficulty acting socially. And some kids are barely able to function at all.

There is a group of people who believe that vaccines are causing ASDs. In this article, we're going to investigate whether or not this hypothesis is valid.

Thimerosal in Vaccines

Some technology, like toilets, we're grateful for, while some, like genetically modified foods, only raise suspicion. And sometimes we're right to be suspicious -- mankind has made mistakes. After all, we used to think lead paint was fine.

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Activist Robert F. Kennedy Jr. speaks at a rally on Capitol Hill calling for "greener" vaccines on June 4, 2008 in
Washington, D.C.

For some people, thimerosal is the new lead paint. Why? Because thimerosal has been used as a preservative in vaccines since the 1930s, and some label the mercury-containing additive as the agent to blame for autism.

Mercury doesn't sound like the kind of substance you want coursing through your veins. The dangers of mercury in fish, for example, have been widely documented. But there's a difference between the kind of mercury in fish and the kind that's found in tiny amounts in vaccines.

Many fish contain methylmercury. People worry about the effects of methylmercury because it bioaccumulates, which means that over time, it becomes more concentrated in the body's tissues. This is why pregnant women are told to monitor their intake of fish. High methylmercury exposure in babies is tied to developmental delays and neurological impairment.

Ethylmercury, on the other hand, is what you find in thimerosal. Why have a mercury-containing chemical in your vaccine? There are two ways to dispense a vaccine: in single-dose or multi-dose vials. The danger of drawing out one dose from a multi-dose vial and then sticking a needle back in for another is contamination from bacteria and other organisms. Thimerosal is a preservative that keeps the vaccine from getting contaminated, so you're not getting a dose of bacteria to boot.

Ethylmercury and methylmercury aren't the same thing. From studies done on monkeys and on vaccinated babies, we know that the two compounds aren't metabolized and excreted the same way, and we know that ethylmercury doesn't seem to bioaccumulate [source: National Network for Immunization Information, NNIii]. But at the time when people began looking for possible autism causes, scientists didn't have this information. So people looked at the recommended limit for methylmercury and realized that the ethylmercury exposure from vaccines might exceed that limit.

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Measles, Mumps, Rubella and Autism

A study done in the 1990s by Andrew Wakefield on 12 children suggested a link between the measles, mumps, rubella (MMR) vaccine and autism. In the years that followed, it came out that Wakefield had a conflict of interest, and some of his co-authors repudiated the results altogether. A study in Japan of more than 30,000 children showed that even after the MMR vaccine was broken into single shots (instead of the usual triple shot), autism rates continued to rise [source: Coghlan]. For more information on the MMR and autism, check out this CDC fact sheet.

�As it turns out, events unfolded messily. Among a flurry of other articles, Robert F. Kennedy Jr. wrote a piece for Salon and Rolling Stone that claimed to expose a government cover-up of the effects of thimerosal in vaccines because of ties to the pharmacy industry. Various autism advocacy groups got involved, as did other writers and doctors, some more reputable than others. The result? Vaccines in the United States today are almost entirely free of thimerosal or contain trace amounts (less than 1 microgram) by mandate of the Food and Drug Administration. The exception is the influenza vaccine, although you can find preservative-free versions. (For more background information on vaccine studies, see these article synopses from the NNii.)

Yet despite the removal of thimerosal from vaccines, autism rates haven't dropped. Denmark removed thimerosal from its vaccines in 1992, and its rates have continued to climb [source: NNii]. There is a possibility that all the money, time and brainpower being thrown into thimerosal-autism studies is wasted -- resources that could be spent trying to find to find the cause of and cure for autism.

Confirmation Bias and the Dangers of the Unvaccinated

If studies continuously debunk these ideas, why do people believe them? It's partly due to the David and Goliath factor -- with the maverick scientist versus Big Pharma/Big Government. When government organizations like the U.S. Food and Drug Administration are tied so closely to drugmakers, their answers (or lack thereof) can seem suspicious. The independent doctor working in his basement promising to find the cause and cure gives a reason to hope.

The Hannah Poling Case

Hannah Poling's family members won compensation for their case that vaccines caused Hannah's autismlike symptoms. The "vaccine court," as it's commonly known, ruled that vaccines might have aggravated an underlying mitochondrial disorder. The vaccines-cause-autism side takes the ruling as vindication, while dissenters maintain that this was a legal ruling and not a scientific or medical one. Stay tuned -- the Omnibus Autism Proceeding is still under way.

But there are unscrupulous people on both sides of the equation. The fact that someone is a regular Joe Schmo, albeit a Dr. Schmo, doesn't mean he or she is immune to the greedy impulses that influence the pharmaceutical companies. You can "follow the money" back to the drugmakers, but you can also follow it back to the lawyers and expert witnesses making a fortune in the Omnibus Autism Hearings and the people peddling expensive "remedies" such as chelation therapy, which removes toxic metals from the body.

It's easy to give in to confirmation bias, which occurs when you find facts that back up your beliefs and reject anything that might force you to reevaluate your stance. Many people also misunderstand correlation versus causation: Just because two events occurred near each other doesn't mean that one caused the other.

Let's say you bring your toddler in for a vaccination and shortly thereafter, your kid gets sick. You might think the vaccine led to his illness, but logically, that line of thought doesn't make sense. If you bought a strawberry ice cream cone with extra sprinkles and promptly tripped and skinned your knee, you wouldn't say that extra sprinkles cause clumsiness. But the very idea of vaccines is scary to some people -- it doesn't seem right to introduce disease in order to protect against it.

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New Yorkers queue up for their free smallpox vaccinations after 12 cases were reported in the state, April 1947.

�The dangers of the growing ranks of the unvaccinated are twofold. First, there's the very real prospect of an unvaccinated child or adult acquiring a disease. Before vaccines eradicated smallpox, it killed millions of people throughout history. According to the World Health Organization, the world saw 50 million cases of smallpox a year as late as the 1950s [source: WHO]. Those who didn't die were scarred for life or often blinded. And smallpox isn't the only vaccine success story. In 1952 in the United States, more than 57,000 people were struck with polio, which can cause paralysis and even death [source: CDC]. After Dr. Jonas Salk's vaccine became available, rates of infection dropped by 85 to 90 percent [source: CDC].

To compound the dangers of getting sick, vaccines also operate on a principle of herd immunity, or community immunity. Basically, the more people within a community who are vaccinated, the greater the chance we all have of fighting an outbreak of disease. Conversely, the more unvaccinated people, the greater the danger of falling prey to an epidemic. Before the measles vaccine became available in the '60s, 450 people died and 4,000 people developed encephalitis a year in the United States alone from a disease that we can now prevent [source: CDC].

And yet from January to July 2008, the Centers for Disease Control and Prevention received reports of 131 cases of measles, the highest number of cases since 1996 [source: CDC].

To learn more about autism and vaccines, follow the links on the next page.

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