THURSDAY, Sept. 4 (HealthDay News) -- Hoping to dispel long-running concerns that autism is linked to the measles-mumps-rubella vaccine (MMR), researchers now say a new study shows the childhood vaccine does not raise that risk.

"We are certain that there's no link between autism and the MMR," Dr. W. Ian Lipkin, director of the Mailman School of Public Health Center for Infection and Immunity at Columbia University College of Physicians and Surgeons, said at a Wednesday teleconference.

"We found no evidence that the [gastrointestinal] pathology consistently preceded autism, and we also found that the MMR didn't consistently precede either autism or GI pathology," he added.

Not everyone is convinced, however, that the vaccine does not play a role in causing gastrointestinal problems that can precede the onset of autism.

"This study addresses one hypothesis. This study, by itself, does not exonerate the role of all vaccines. There are many biological mechanisms where environmental factors could present in the development of autism," said Rick Rollens, the father of an autistic son and one of the founding members of the M.I.N.D. Institute at the University of California, Davis. Rollens was also part of the teleconference.

Before the measles vaccine was introduced in 1963, between 3 million and 4 million Americans contracted the measles each year, and about 400 to 500 people died annually, according to background information provided by the researchers.

In 1998, a small British study linked the presence of measles RNA in the gastrointestinal tract and children who had autism and gastrointestinal (GI) problems, which seemed to confirm what many parents of children with autism had suspected all along -- that the vaccine played a role in the development of autism.

To investigate this possible link, researchers from Columbia University Mailman School of Public Health, the U.S. Centers for Disease Control and Prevention, Massachusetts General Hospital and Trinity College Dublin in Ireland used tissue biopsies taken from the bowels of children with autism and GI problems and compared them to age-matched control children who had no developmental delays, but were undergoing bowel biopsies for GI disturbances. The control group children also were matched as closely as possible with regard to when they received their MMR vaccine.

The researchers used techniques similar to those used by the British scientists a decade ago. But advances in technology since then make molecular analysis more sensitive now, the study authors said.

The researchers analyzed the bowel tissue to look for the presence of measles virus RNA. One theory held that the measles RNA could grow in the intestinal tract and cause inflammation that would make the bowel more permeable. Once the bowel was more permeable, the virus could enter the circulation system and then travel to the central nervous system, where it might play a role in the development of autism, some theorized.

However, only one child out of the 25 children with autism and one in the control group of 13 children in the new study showed slight levels of measles RNA. According to one of the study's authors, Dr. Mady Hornig, director of translational research at the Mailman School of Public Health Center for Infection and Immunity, the levels of measles RNA was just above the threshold levels.

The new findings were published online Thursday in the Public Library of Science journal.

"This was a rigorous analysis. We did this in a blinded fashion, and we are persuaded that there is no link," Lipkin said.

He added that these findings don't mean that the occasional child won't have an "idiosyncratic response" to the vaccine. "Nothing is without risk," he said.

Rollens, however, remains steadfast in his belief that immunization played some role in his son's autism. "I'm totally convinced the vaccines caused the autism of my son, and we need to have more biological studies on this vaccine and others," he said.

More information

To learn more about research on vaccines and autism, visit the U.S. Centers for Disease Control and Prevention.