Controversial Study Withdrawn Suggesting Link Between Autism and MMR Vaccine

March 9, 2004

In 1998, Andrew Wakefield headed a group of researchers in publishing a much-disputed study that suggested a possible link between autism and the measles-mumps-rubella (MMR) vaccine. Since then, several studies have found no clear evidence to link MMR and autism, and all major health organizations - including the American Academy of Pediatrics, the National Institutes of Health, the Centers for Disease Control and Prevention, and the World Health Organization - have rejected Dr. Wakefield's claims. Still, fear of the MMR vaccine has caused some parents to avoid immunizing their children, leaving them susceptible to diseases that once killed thousands.

Now, 10 out of its 13 authors are retracting, or taking back, the controversial 1998 study. The Lancet, the journal in which the 1998 study was published, printed the retraction in the March 6 issue. The authors write: "We wish to make it clear that in this paper no causal link was established between MMR vaccine and autism as the data were insufficient. However, the possibility of such a link was raised and consequent events have had major implications for public health. In view of this, we consider now is the appropriate time that we should together formally retract the interpretation placed upon these findings in the paper."

Dr. Wakefield, who did not sign the retraction, believes that the MMR vaccine causes abnormalities in the intestines that lead to the release of toxic chemicals that cause autism when they reach the brain. However, most medical experts have agreed for years that his study is critically flawed. The most notable problems with Dr. Wakefield's 1998 study were that it:

• involved only 12 children - not a large enough sampling to generalize to the entire population
• didn't use a control group - that is, it only studied autism in vaccinated children, and didn't compare the incidence of the condition in unvaccinated children
• proposed a link between the timing of the MMR vaccine and the onset of symptoms of autism without addressing two issues: one, that because MMR is given around the time that autism is commonly diagnosed (12 to 15 months), the association of the vaccine to the symptoms might be coincidental; and two, that in several of the studied children the symptoms of autism pre-dated the vaccination

About Autism
Autism is a developmental disorder that affects as many as one in 500 people in the United States. Usually diagnosed in toddlers, it's characterized by mild to severe impairment of communication and social interaction skills. Although a specific cause of autism has not been found, several theories exist.

Although the number of children diagnosed with autism is increasing, the rates of MMR vaccination are not; in London, diagnosis of autistic disorders has been on the rise since 1979 but hasn't increased since routine MMR vaccination began in 1988. In addition, the age of diagnosis of autism has been found to be the same whether a child receives the MMR vaccine or doesn't. What many researchers are discovering is that subtle symptoms of autism are often present before a child's first birthday - sometimes even in early infancy - but often go unnoticed until the symptoms are more obvious to parents.

So what could explain the increased rates of autism in recent years? For one thing, a broader definition of autism that can be applied to more children who show varying degrees of symptoms. There's also been a greater awareness of the condition among health professionals, which has lead to more diagnoses.

As for what causes the condition, medical experts believe it may be a combination of factors. A genetic basis is suspected, evidenced by the fact that the identical twin of a child with an autistic disorder will have a 92% chance of having one, too, while a fraternal twin has only a 10% chance. Research also points to the possibility that other factors, such as toxins or viral infections, may cause or trigger autism before birth.

Medical researchers all over the world continue to investigate the possible causes of autism.

Reviewed by: Steven Dowshen, MD
Date reviewed: March 2004

Printer-friendly version Email this article to a friend Send email to us