Is There a Link Between Vaccines and Autism?

In the absence of hard evidence, how to make an informed decision.

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I belong to a local parenting "listserv," where moms and dads share information on everything from breastfeeding and circumcision to tantrums and teething. Over the past few weeks, there's been a persistent topic of both curiosity and debate roiling through our group's e-mails: vaccine slowdown.

Vaccine slowdown, or spreading out the number of shots given to babies and toddlers over several doctor visits, has become a growing phenomenon and a white-hot issue among parents. This idea was sparked by the continuing concern that the shots kids get during childhood cause autism—the devastating spectrum of developmental disorders that can trigger severe problems with a child's speech, behavior, socialization and motor skills.

Before you decide what's best for your children, it's important to know all the facts.

The idea that the very vaccines that are designed to protect our kids against serious, life-threatening diseases like polio, measles and tetanus might actually harm them is not new. And neither is the fear that autism is linked to immunization. However, time and again major studies have found no connection between vaccinations and autism. The American Academy of Pediatrics (AAP) and other mainstream medical organizations have reported repeatedly that there is no proven association.

"My best friend's brother is autistic, so I am very empathetic to a family's struggle with autism," says Sharon Denise Allison-Ottey, a physician and executive director of the COSHAR Foundation, a national organization dedicated to improving health awareness. The foundation hosts "Immunization Sundays" in African-American churches to raise consciousness about the importance of vaccines. "Certainly any parent wants to protect their children," says Allison-Ottey, "and the best way to do that is by vaccinating children from preventable diseases that are life-threatening."

So in the face of science, why does this fear of immunization persist? First, it's a numbers game. Autism diagnoses have skyrocketed since the 1990s. The Centers for Disease Control and Prevention has estimated that one in 150 children—most often boys—have some form of it. It is not clear if the mounting rates are due to a change in the definition of the disease, an improved ability to diagnose it or an actual increase in illness, but, according to the Autism Society of America, it is now the nation's fastest-growing developmental disability.

At the same time that autism and related disorders have exploded, so has the number of shots given to children. Back in the 1940s, only one vaccine—smallpox—was administered routinely. (Of course, in those days, children contracted all kinds of diseases, including polio, and many died.) Now, by the age of 12, most kids will have received 30 to 35 doses of vaccines to protect against 34 diseases.

Maybe it's just bad timing, but symptoms of autism and other developmental disorders often show up before age 2—right around the time very young children get the bulk of their vaccinations. Horror stories abound—especially on the Web—of children who begin to show developmental delays right after they've gotten immunized. Is this a terrible coincidence, or did those shots cause the problem? No one knows for sure.

"If a child has a genetic predisposition to autism, signs of the disease would be revealing themselves at the same time that child would be getting another series of vaccines," says. Allison-Ottey. "But at this point, there is no way to tell which came first."

How exactly could a shot or series of shots cause autism? In the past, the worry was that thimerosal, a mercury-based preservative used in vaccines, might be the culprit. As a precautionary measure, in 1999, the AAP asked manufacturers to remove thimerosal from all pediatric vaccines, and it has not been used in shots given to kids since 2001. Nonetheless, autism cases have continued to rise.