The idea was that the measles virus from the live-virus measles vaccine lurks in the gut of some young children, causing bowel disease and making them more susceptible to environmental factors that might cause autism.
Now a painstaking, six-year study of children with bowel disease -- 25 with autism and 13 with normal development -- shows no link between getting the MMR (measles-mumps-rubella) vaccine and either autism or bowel disease.
"We are convinced there is no link between MMR vaccination and autism," study leader W. Ian Lipkin, MD, director of the center for infection and immunity at Columbia University's Mailman School of Public Health, said at a news conference.
Lipkin was quick to add that the current study focuses only on theories that the MMR vaccine causes autism. It does not address other vaccine-autism theories, such as the fear that the mercury-containing preservative thimerosal might cause autism. The MMR vaccine does not contain thimerosal.
It's a "fabulous" and "terrific" study, says William Schaffner, MD, president-elect of the National Foundation for Infectious Diseases and chairman of the department of preventive medicine at Vanderbilt University. Schaffner was not involved in the study.
"This really closes the scientific inquiry into whether measles or MMR vaccination causes autism," Schaffner tells WebMD. "It is convincing because it takes the original concept of the profoundly flawed [earlier] study and does it the way it should have been done the first time."
That earlier 1998 study by U.K. researcher Andrew Wakefield and colleagues first put forward the theory that measles viruses lurking in the gut might cause autism. However, most members of this research team later retracted their findings.
A 2002 study purportedly found measles-vaccine virus in the intestines of kids with autism and bowel disease -- but not in developmentally normal kids.
Some of those same researchers participated in the Lipkin study. The new study, repeating tests in multiple laboratories and using state-of-the-art technology, found slight traces of measles-vaccine virus in only two kids. One of these children had autism, the other did not.
Moreover, only five of the 25 kids with autism got their MMR vaccine before getting bowel disease and autism.
Autism and Intestinal Disease
Importantly, Lipkin said the study confirmed that kids with autism often have "unrecognized and undertreated bowel complaints." He credited Wakefield with being the "first to recognize the importance of gastrointestinal disease in autism," but insisted that MMR vaccination cannot account for this.
These intestinal problems may well be linked to the developmental regression seen in about 25% of kids with autism. Some of these children appear developmentally normal and then slide into autism. Others may have mild autism symptoms and then become much more disabled, says study researcher Mady Hornig, MD, director of translational research at Columbia's Mailman School of Public Health.
"The proportion of children with bowel disease and developmental regression underscores the possibility that this subset of kids with autism and intestinal problems may have separate problems that each contribute to their illness," Hornig said at the news conference.
That's a welcome thing to hear from mainstream researchers, says Sallie Bernard, executive director of SafeMinds, an autism-advocacy organization.
"On the plus side, this study has shown a link between gastrointestinal distress and regression in autism," Bernard tells WebMD. "A lot of people don't accept this and deny parents' perspective when they say their kids' with autism have GI trouble."
But Bernard says the Lipkin study does not close the book on the theory that MMR vaccine might trigger autism.
She notes that autism embraces a wide range of disorders likely caused or made worse by different factors. And the Lipkin study, Bernard says, was too small to clear MMR vaccination as a possible factor.
"I do see that some of the study authors, whom I like a lot, want to put MMR to rest as one of these factors. I respectfully disagree," she says. "I think it is premature to discount MMR from a study of this size. It is not a big enough sample to understand if there is a subgroup in which MMR is exacerbating or leading to the gastrointestinal inflammations we see in these children."
Lipkin and colleagues report their findings in the Sept. 4 issue of the online journal PloS One.