Autism and the MMR Vaccine Connection

by National Institute of Health

What is autism?

Autism is a complex biological disorder of development that lasts throughout a person's life. People with autism have problems with social interaction and communication, so they may have trouble having a conversation with you, or they may not look you in the eye. They sometimes have behaviors that they have to do or that they do over and over, like not being able to listen until their pencils are lined up or saying the same sentence again and again. They may flap their arms to tell you they are happy, or they might hurt themselves to tell you they are not.

One person with autism may have different symptoms, show different behaviors, and come from different environments than others with autism. Because of these differences, doctors now think of autism as a "spectrum" disorder, or a group of disorders with a range of similar features. Doctors classify people with autism spectrum disorder (ASD) based on their autistic symptoms. A person with mild autistic symptoms is at one end of the spectrum. A person with more serious symptoms of autism is at the other end of the spectrum. But they both have a form of ASD.

Why do people think that vaccines can cause autism?

Some parents and families of children with autism believe that the Measles/Mumps/ Rubella (MMR) vaccine caused their children's autism. These parents report that their children were "normal" until they received the MMR vaccine. Then, after getting the vaccine, their children started showing symptoms of autism. Because the symptoms of autism begin to occur around the same time as the child's MMR vaccination, parents and families see the vaccine as the cause of the autism. However, just because the events happen around the same time does not mean that one caused the other. Although children receive many other vaccines in addition to the MMR vaccine, these other vaccines have not been identified as possible causes of autism.

These parents' beliefs and observations were reinforced by a small study of bowel disease and autism, published by Wakefield and his colleagues in 1998. The study's authors suggested that there was a link between the MMR vaccine and autism. This study did not include scientific testing to find out if there was a link.The authors relied on the reports of parents and families of the 12 children with autism involved in the study to make their suggestion. The study did not provide scientific proof that there was any link.

Since this study was published in 1998, a number of other studies have also been published that suggested a link between the MMR vaccine and autism, but none of these provide scientific proof of such a link.

To date there is no definite, scientific proof that any vaccine or combination of vaccines can cause autism. It's important to know that vaccines actually help the immune system to defend the body.

How do vaccines help the immune system defend the body?

The immune system has cells, sometimes called memory cells, that remember diseases. If these cells meet a disease, they keep track of what it looks like so they can recognize it later.W hen the memory cells meet up with the disease again, they recognize it and know they need to get rid of it. They call in the other parts of the immune system to get rid of the disease. In some cases, memory cells can recognize a disease without ever having to meet up with it, which is called "natural" immunity. In other cases, the cells need some help to become familiar with a disease.

That help comes in the form of a vaccine. The vaccine takes a form of the disease that doesn't make you sick and introduces it to the memory cells so they know what to look for later. If the memory cells ever bump into the disease again, they know to call in other cells in the immune system to protect the body and get rid of the disease. The memory cells of a child keep track of diseases well into adulthood, preventing such diseases by getting rid of them quickly. In this way, vaccines help the immune system by making it easier to remember diseases.

Why do many doctors and scientists believe that the MMR vaccine does not cause autism?

In 2000, the Institute of Medicine (IOM) at the National Academy of Sciences, at the request of the Centers for Disease Control and Prevention (CDC) and the NIH, conducted a review of all the evidence related to the MMR vaccine and autism. This independent panel examined completed studies, on-going studies, published medical and scientific papers, and expert testimony to assess whether or not there was a link between autism and the MMR vaccine. The IOM concluded that the evidence reviewed did not support an association between autism and the MMR vaccine. This and other conclusions from the IOM review were released in April 2001.

Also in 2000, The American Academy of Pediatrics (AAP), a professional organization for pediatricians with over 55,000 members, held a conference on the MMR vaccine and autism. Parents, scientists, and practitioners presented information on this topic to a multidisciplinary panel of experts. Based on its review, the AAP also found that the available evidence did not support the theory that the MMR vaccine caused autism or related disorders. The AAP policy statement appeared in the May issue of Pediatrics.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.