Study Finds No Link Between MMR Vaccine and Autism

A study of 500,000 Danish children has found no link between receiving the measles-mumps-rubella vaccine and developing the devastating childhood disorder known as autism.

The study, published today in the New England Journal of Medicine, is the latest of several studies to negate the suspicion, held by many parents, that the MMR vaccine is behind the recent dramatic rise in autism cases. In California, the number of autistic children receiving services from the state’s Department of Developmental Services climbed 273% between 1987 and 1998.

Although the study is from Denmark, it is relevant for the United States, the authors said. The two countries use the same MMR vaccine and use very similar medical criteria for diagnosing autistic children.

Earlier studies had concluded there is no evidence of a MMR-autism link. But several scientists said the study was particularly powerful because it was so large and allowed researchers to track children individually.

All residents of Denmark are given an identification number, and later medical events such as vaccinations and psychiatric diagnoses are routinely recorded.

The study, led by epidemiologist Dr. Kreesten Meldgaard Madsen of the Danish Epidemiology Science Center, analyzed data for all Danish children born between January 1991 and December 1998.

Of those 537,303 children, 440,655 had received an MMR vaccine and 96,648 had not. A total of 316 had been diagnosed with autistic disorder, and 422 had been diagnosed with other, closely related conditions collectively known as autism spectrum disorders.

Analyzing the data, the scientists found that children who had been vaccinated were statistically no more likely to develop autism than children who had not been vaccinated.

The study was co-authored by scientists at the Danish center in Aarhus and Copenhagen, and the U.S. Centers for Disease Control and Prevention in Atlanta.

“I hope the study finally lays to rest the idea that the MMR vaccine causes autism,” said Dr. Jay M. Lieberman, chief of pediatric infectious diseases at Miller Children’s Hospital in Long Beach. Lieberman said that he has been troubled by an increase in the numbers of parents refusing the MMR vaccination out of fears that it will hurt their children.

Measles kills about 600,000 people worldwide each year, Lieberman said. It killed more than 140 people in the United States during a 1989-91 outbreak caused by inadequate vaccination among schoolchildren. Rubella causes birth defects when it infects pregnant women, and was once a leading cause of deafness in the U.S. before MMR vaccinations became routine.

Scientists are still seeking an explanation for the apparent rise in autism cases. They know that genetics is involved -- autism tends to run in families -- and have narrowed down the location of some of the possible genes. Because the rate of the disorder appears to have risen, scientists are also investigating possible environmental factors such as exposure to thimerosal, a mercury-based preservative used in some vaccines. The MMR vaccine does not contain thimerosal.

But many scientists still suspect that at least some of the seeming rise is due to increased diagnosis instead of an actual increase. Parents, teachers and doctors are all far more aware of autism than in years past, said Catherine Lord, professor of psychology and psychiatry at the University of Michigan.

A recent UC Davis study concluded that the steep increase in California cases could not be explained in this fashion. Until larger-scale surveys are undertaken, “I think we just don’t know,” Lord said.

Parent activists who strongly suspect an MMR-autism link say the Danish study still does not lay the matter to rest.

“I’m not at all convinced by it,” said Bernard Rimland, director of the Autism Research Institute in San Diego.

Rimland said that rates of autism in the Danish study were lower than those in the U.S., leading him to suspect that data could not be extrapolated to the U.S. situation.

Liz Birt, a Chicago-based activist and mother of an autistic child, said the study was flawed because it did not look at the effect of the MMR vaccine on a certain type of autism that she believes is linked.