Do Vaccines Cause Autism?
Do Vaccines Cause Autism?
There are many theories about a possible link between autism and childhood vaccines. Learn what the latest research shows about this controversial topic.
By Diana Rodriguez
Medically Reviewed by Pat F. Bass III, MD, MPH
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The controversial subject about a potential link between autism and vaccines made an appearance at the second GOP debate on September 16, 2015.
For parents, each of their child’s developmental milestones — a first word or first step — is a source of joy mixed with a dose of relief that their child is progressing normally. Any variation in a child’s development can become a cause for alarm, and the specter of autism looms large in these fears.
With the number of autism cases on the rise, many parents are concerned over theories that childhood vaccines may play a role in causing this developmental disability. Find out what an expert and a parent have to say.
The Autism-Vaccine Myth
Today, approximately 1 in 68 children is diagnosed with autism spectrum disorder (ASD), according to the Centers for Disease Control and Prevention (CDC), up considerably from 2000, when that statistic was 1 in 150. While the diagnoses are rising, doctors and researchers aren't exactly sure why. One possible reason is that autism is being identified more frequently, as a full or partial diagnosis (as in the case of a child being diagnosed with both intellectual disability and autistic features), says Julia A. McMillan, MD, a professor of pediatrics and an infectious disease specialist at Johns Hopkins Children's Center in Baltimore.
"The diagnosis is simply being made using much broader criteria than in the past," Dr. McMillan says. The other possible explanation is that autism is more often reported than in recent years, perhaps because of special assistance that's now available for autistic children.
But one theory that's been discussed and studied all over the world is that the rise in autism has something to do with the increase in childhood vaccinations. Why? The controversy was ignited in 1998 by a small study in the journal The Lancet based on reports from parents of 12 children with autism. In the study, a physician in England claimed to have evidence showing a relationship between autism and a combination childhood vaccine — MMR, or measles, mumps, and rubella. That claim has since been widely discredited.
"That work has been retracted and disclaimed," McMillan says. Time and time again, in many studies all over the world, the theory has been proven untrue. The Institute of Medicine, which conducted research reviewing any potential link between vaccines and autism, states that there is no evidence to support such a link, and the CDC supports that statement.
The Research Is in: Vaccines Do Not Cause Autism
Another reason why parents and some doctors thought childhood vaccines might be one of the potential causes of autism is that they used to contain a mercury-based preservative called thimerosal. While no studies showed a link between any harmful side effects and the thimerosal in vaccines, the American Academy of Pediatrics and several federal government health agencies recommended in 1999 that thimerosal be removed from childhood vaccines, and for the most part that has occurred, according to the Food and Drug Administration. Today, no recommended childhood vaccine used in the United States contains it, except some influenza vaccines, McMillan says.
According to McMillan, the mercury contained in thimerosal is different from the methyl mercury found in nature and even in many fish that people eat. Methyl mercury in large amounts can have harmful side effects, resulting in intellectual and mental health problems, but McMillan says there's no evidence that the mercury contained in thimerosal and present in very small amounts as a preservative in some influenza vaccines is harmful. As McMillan reiterates, "Many scientific studies have shown that there's no relationship between thimerosal and autism, and, importantly, the MMR vaccine never contained thimerosal."
RELATED: Where Did the Myth About Vaccines and Autism Come From?
Numerous studies conducted across the globe have tracked autism statistics both before and after the removal of thimerosal from childhood vaccines. The results show that the rate of autism cases rose even after thimerosal's removal. Though it’s still possible to find the occasional study showing evidence that a link between childhood vaccines and autism could be possible, the majority of experts say that the theory just isn't backed up with good scientific evidence.
A large new study published in The Journal of the American Medical Association found no link between MMR vaccination and the development of autism. The study, which was the largest of its kind to date, looked at more than 95,000 children who did and did not receive the MMR vaccine. Even in high-risk families — those who have an older child with autism — there was no association.
A Parent's Viewpoint
The undeniable fact is that no one knows what causes autism. So, say skeptics, how can experts claim to know what doesn't cause it? When you’re the parent of a healthy, developing toddler who suddenly backslides after vaccinations, the evidence can be tough to swallow.
Jennifer Parido, of Frankfort, Kentucky, says that the timing of her daughter Chloe’s autism symptoms made her suspicious that vaccines played a role. “I noticed signs of differences in Chloe after her 12-month-old shots,” Parido says of her daughter, who has a twin sister. “She was the first to talk, first to walk, first to wave bye-bye out of our set of twins, and then all of a sudden these things began to disappear.”
The changes were drastic. “It was as if all of these milestones disappeared overnight,” Parido says. As Chloe's twin, Riley, continued to meet her developmental milestones, Chloe did not. Instead, she regressed. “It wasn't until she was 3 years old that I actually heard her say 'mama' for the first time,” Parido says.
No doctor has ever indicated that her daughter’s vaccines could have played a role in her autism, but she and her husband are suspicious that they contributed to some degree. Yet this hasn't turned Parido against vaccines.
“We still do vaccinate our children and believe that they are important in eliminating childhood disease and sickness,” she says.
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