CDC Study Finds No Link Between Number of Vaccines and Autism

by Kayt Sukel

May 28, 2013

The similarities in the stories were striking. As clinicians puzzled over why the number of autism cases grew so dramatically, many parents reported that their children’s symptoms coincided with vaccinations.

“There was a widespread narrative for a while—parents would say that they had a child that seemed to be developing perfectly normally but then, after a vaccine, that child would run a fever, get a little delirious, and never return to that original schedule of development. That’s how the parents described the onset of their child’s autism,” says Irva Hertz-Picciotto, an environmental epidemiologist at the University of California Davis who studies environmental factors contributing to autism. “And many of the studies looking at the vaccine question came from these stories.”

In the past decade, researchers at independent research institutions and universities as well as the Centers for Disease Control and Prevention (CDC) have looked at different facets of the so-called “vaccine question” and found all without proof. Previous work that seemed to link a specific vaccine—the measles, mumps and rubella (MMR) shot—to autism was debunked in a series of studies. Studies that examined whether thimerosal, a mercury-based preservative used in some vaccines, played a role found no link. And, now, Frank DeStefano, director of the CDC’s Immunization Safety Office, and colleagues have demonstrated that the number of antigens, the substances in vaccines that trigger the antibody immune response, received over the course of the recommended vaccine schedule is not associated with autism, either.

To look at the “too many vaccines too soon” hypothesis, DeStefano and colleagues looked at the records of approximately 1,000 served by three managed care organizations  Approximately one-fourth of the children had been diagnosed with autism spectrum disorder (ASD). The researchers looked at both each child’s cumulative exposure to the vaccine antigens as well as the maximum number of antigens each child received in a single day. The results were published on March 29 in the Journal of Pediatrics.

“Each vaccine has a different number of antigens. So you can’t count just the number of vaccines. That doesn’t tell you what you need to know. So we counted the number of antigens in each vaccine and totaled them up,” says DeStefano. “And we found no difference in the amount of vaccine antigens that these groups of children, those who had autism and those who didn’t, had been exposed to either in a single day or over the first two years of life.”

While some have argued that this study answers the “vaccine question” once and for all, some autism organizations still say that there still may be some risk. Autism Speaks, a national organization that advocates for finding cures for the disorder, recommends on its website that children be vaccinated. However, its website also cautions, “It remains possible that, in rare cases, immunization may trigger of the onset of autism symptoms in a child with an underlying medical or genetic condition.”

 “Our voice is very loud in that we support the vaccine schedule and that we feel the evidence has said there is no elevated risk for autism in the general population,” says Alycia Halladay, the organization’s senior director of environmental and clinical sciences. “But there is still the possibility that vaccines may have adverse events. So our main message is that parents should talk to their doctors about vaccinations, get as much information as they can and make an informed decision from there.”

DeStefano agrees that parents should talk to their physicians about vaccinations—and he also says he is not surprised that the idea of a vaccine/autism link perseveres. “One-quarter to one-third of parents have concerns about vaccines and the possible development of autism. It’s a persistent issue. But this study provides additional evidence to assure parents that vaccines are safe,” he says.

“But the real thing I want to emphasize, however, is that one of the most important things parents can do to protect and maintain the health of their young children is to get them vaccinated, according to the recommended schedule. ” 

Vaccines prevent infectious diseases in those who receive them, and protect them and others who come in contact with unvaccinated, infected people. Vaccinating children against diseases helps protect both their health and the community's health.