Doubt cast on causal link between MMR vaccine and autism

No change is called for in administering the current measles, mumps and rubella vaccine, a new IOM report concludes.

By Susan J. Landers, amednews staff. May 14, 2001.

Washington -- A new Institute of Medicine report has failed to find any apparent link between the measles, mumps and rubella vaccine and autism.

The evidence reviewed by a 15-member committee "favors rejection of a causal relationship at the population level between MMR vaccine and autistic spectrum disorders," said committee Chair Marie McCormick, MD, ScD, professor and chair of Harvard's Dept. of Maternal and Child Health. The committee released its findings April 23.

Links

However, Dr. McCormick left open the possibility that the MMR vaccine could, "in rare cases," contribute to the development of autism in a small number of children.

"We do not have epidemiological data or tools precise enough to assess rare occurrences of such a response to MMR, if it occurs at all," she said.

The committee recommended that current MMR immunization procedures continue to be followed.

The IOM report is not alone in failing to find a link between the MMR vaccine and autism, notes Bruce Gellin, MD, executive director of the National Network for Immunization Information.

In addition, Medical Research Council in Great Britain released a report and the American Academy of Pediatrics is set to release another report, both discounting a link between the vaccine and autism.

It is this growing body of scientific evidence that will affect what people do, Dr. Gellin said.

Concerns still exist

But the findings do not put to rest parents' concerns that a link exists between the MMR vaccine and autism. Parents say their children develop normally until they are vaccinated at 15 to 18 months. Shortly afterwards, parents say, they notice pronounced regression in their child's speech and behavior that ultimately leads to a diagnosis of autism.

Members of one parent advocacy group, the National Vaccine Information Center, express fear that only part of the IOM report would be heard by policymakers and others.

"The committee clearly acknowledged the biologic plausibility that MMR vaccine could be a cofactor in causing autism in some children," said Barbara Loe Fisher, the Center's president. "But the message the report may send out in practical terms is that there is absolutely no association between vaccination and autism, and the case is closed."

The group has pressed for scientific research into the possibility that vaccines are associated with not only autism but also learning disabilities, attention-deficit/hyperactivity disorder, asthma and other chronic neuroimmune disorders.

Fueling the belief that the MMR vaccine may trigger cases of autism has been a dramatic increase in the number of children who have been diagnosed with autism since the vaccine was first introduced.

Pediatricians have called for continued and aggressive research into the causes of autism, said AAP President Steve Berman, MD. Autism is a very serious but poorly understood condition that could be related to a number of factors, he said.

At the same time, he said, "current scientific evidence indicates that vaccines are not the cause."

AAP continues to recommend that parents fully vaccinate their children to prevent the spread of potentially dangerous diseases, Dr. Berman said.

The MMR vaccine, which contains three vaccines in a single shot, has virtually eliminated measles, mumps and rubella in the United States, Dr. McCormick noted. Measles cases have dropped from more than 400,000 per year in the pre-vaccine era to only 100 in 1999.

In reaching its conclusion, the IOM committee considered the debate in a broader social context, according to Dr. McCormick. "If left unchecked, infectious diseases like measles, mumps and rubella could cause considerable sickness and death," she said.

Public health officials feared a repeat of a 1970s situation in which concerns about the safety of the pertussis vaccine caused many to forgo immunization, Dr. McCormick said. The result was a rebound of pertussis cases.

"Similarly devastating disease outbreaks could easily occur again, if immunization rates were to decline as a result of fears regarding MMR," she said.

Dr. McCormick also testified about the report's conclusions before the House Government Reform Committee. The April 25 and 26 hearings were held by Committee Chair Dan Burton (R, Ind.) to examine increasing autism rates.

Burton held similar hearings in the previous Congress.

The congressman's grandson, who is now autistic, was developing normally until receiving his vaccines, Burton said. The hearings have been an attempt, he said, to uncover the cause: whether it was the MMR vaccine, elevated levels of mercury in the vaccine or something else entirely.

Dr. McCormick told the panel that scientists generally agree that most cases of autism result from events that occur prenatally or shortly after birth. But the MMR vaccine is administered in a child's second year, she said, about the same time that autistic symptoms become apparent.

She also told the panel that to evaluate the hypothesis connecting the MMR vaccine and autism, her committee reviewed all published, peer-reviewed scientific and medical literature and held an open scientific meeting that included a broad group of researchers and vaccine safety advocates. In addition, a working group of the committee conferred with the parents of autistic children and vaccine safety advocates to discuss their concerns.

ADDITIONAL INFORMATION:

Weblink

Summary of IOM report, "Immunization Safety Review: Measles-Mumps-Rubella Vaccine and Autism."
(http://www.iom.edu/IOM/IOMHome.nsf/Pages/MMR+Autism+Summary/)