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IOM Report Discounts Link between MMR Vaccine Use and Autism

The controversial theory that the measles-mumps-rubella vaccine (MMR) routinely given to young children is responsible for the rise in the incidence of autism in recent years has no scientific basis, according to a report released late in April by a panel convened by the Institute of Medicine (IOM). After reviewing published studies that analyze potential relationships between MMR vaccine use and autism, the panel’s 15 experts conclude that there is no "causal relationship at the population level" while cautioning that epidemiological studies cannot rule out the possibility that the vaccine adversely affects small numbers of children. Nonetheless, the IOM report recommends that the issue receive "continued attention," noting that the analysis "does not exclude the possibility" that the vaccine "sometimes results in the development of autism in a small number of children."

Regardless of this slim possibility, the benefits of the vaccines vastly outweigh potential risks, according to the IOM panel members. "Historically, concerns about the safety of vaccines have led to declines in immunization coverage rates followed by outbreaks of disease, as observed with pertussis in the United Kingdom during the 1970s," their report notes. "Similar outbreaks could easily occur were immunization rates to decline as a result of fears regarding MMR." The National Institutes of Health and the Centers for Disease Control and Prevention commissioned the study by the IOM, which is part of the National Academy of Sciences (NAS) in Washington, D.C.

The IOM panel members based their conclusions about the safety of the MMR vaccine on several factors, including epidemiological studies showing no link between its use and autism incidence within the population, and also failure of any lab experiments to disclose a reasonable biological mechanism that would be consistent with such a link. For instance, many parents who criticize the vaccine cite findings released by the California Department of Developmental Services that indicate a sharp rise in autism cases in the state between 1987 and 1998. Thus, a total of 11,995 autistic children enrolled in the department’s 21 regional programs in 1998, a 210% increase compared with the 3,864 enrolled in 1987. But that increase occurred well after the licensure and introduction of MMR in the United States in 1971, according to the IOM report. "Published studies of trends have been unable to resolve how much of the observed increase is real or due to other factors, such as reporting bias, changes in diagnostic criteria, or better case ascertainment over time." The IOM panel also discounted a 1998 report from Andrew Wakefield of the Royal Free Hospital in London, England. He claimed to have identified a group of a dozen children who developed autism and gastrointestinal symptoms after receiving the vaccine.

Critics who believe that the vaccine harmed their children were quick to zero in on the IOM panel’s call for more research and the fact that it did not definitively rule out a connection. "This is a vindication for those of us who have been trying to get mainstream medicine to take a look at this issue"says Rick Rollins of Granite Bay, Calif., a parent advocate who was instrumental in the creation of an autism research institute at the University of California, Davis. "The jury is still out."

Release of the IOM report coincided with a Congressional hearing on this subject that was convened by Representative Dan Burton (R-Ind.), who is chairman of the House Government Reform Committee. His interest in investigating potential connections between MMR vaccine use and autism is spurred by stories such as Rollins’ and an experience within his own family. According to Rep. Burton, his grandson Christian "was locked into a world of autism" within 10 days of being vaccinated amid an otherwise normal early childhood. "Some would have us believe that a child’s regression into autism within a short time of vaccination is purely a coincidence," Burton says. "I ask those individuals to show me the science that proves their theory." Referring to the IOM report, he says that the panel "found that there was insufficient evidence to conclusively prove or disprove a connection between the MMR vaccine and acquired autism."

The IOM report, one of a series on the health effects of immunization, was issued by a committee whose members are health care professionals selected to exclude any who have a financial or advisory connection with vaccine manufacturers. In previous IOM vaccine-safety studies from 1991 and 1994, the committee was explicitly limited to considering causality and recommending future research directions, whereas for this study it was asked also to evaluate the issue in broader societal terms.

MMR vaccine use is required in all 50 states before a child is admitted to public schools or day care centers. The vaccine has been credited with generally curbing these three once-common pediatric illnesses. Measles cases, for example, have decreased from about 400,000 a year to only 100 in 1999. In other countries where the vaccine is not used, measles accounts worldwide for about 1 million deaths per year.

Marlene Cimons
Marlene Cimons is a Washington reporter for the Los Angeles Times covering health policy.