CHICAGO Scientists who tried to replicate a study that once tied a measles vaccine with autism said on Wednesday they could not find any link and hope their study will encourage parents to vaccinate their children to combat a rash of measles outbreaks.
Parents' refusals to have their children vaccinated against measles have contributed to the highest numbers of cases seen in the United States and parts of Europe in many years.
Measles kills about 250,000 people a year globally, mostly children in poor nations.
Public health officials have been stressing the safety of the combined measles-mumps-rubella, or MMR, shot and other childhood vaccines in the face of vocal groups who claim the immunizations may cause autism and other problems.
The U.S. Institute of Medicine has issued several definitive reports showing no connection between autism and any vaccinations.
This study took a new tack. It attempted to replicate 1998 research by a team led by Dr. Andrew Wakefield, then of Britain's Royal Free Hospital, in the Lancet medical journal that suggested the vaccine was linked to autism and gastrointestinal problems.
Wakefield is undergoing disciplinary action for professional misconduct by Britain's General Medical Council and 10 of his collaborators formally withdrew their original Lancet study.
Scientists at Columbia University in New York and the U.S. Centers for Disease Control and Prevention in Atlanta looked for evidence of genetic material from the measles virus in intestinal tissue samples taken from 25 children with autism who also had GI problems. They compared these to samples from 13 children of similar ages who had GI problems but no autism.
The samples were analyzed in three laboratories that were not told which came from the children with autism. One of the labs had been involved in the original study suggesting a link between measles virus and autism.
"We found no difference in children who had GI complaints and no autism and children who had autism but no GI complaints," Dr. Ian Lipkin of Columbia University told reporters in a telephone briefing.
The team also collected data about the children's health and immunization histories from parents and physicians to see if vaccinations preceded either their autism or bowel trouble.
"We found no relationship between the timing of MMR vaccine and the onset of either GI complaints or autism," Dr. Mady Hornig, also of Columbia, said in a statement.
But the study did find evidence that children with autism have persistent bowel troubles that should be addressed.
"No longer can mainstream medicine ignore parents' claims of clinically significant GI distress," said Rick Rollens, a parent and autism research advocate.
He commended the researchers for their work but said, "This study by itself does not exonerate the role of all vaccines."
The CDC estimates that about one in every 150 children has autism or a related disorder such as Asperger's syndrome -- 560,000 people up to age 21 in the United States.
The findings, reported in the journal Public Library of Science, can be found here
(Editing by Maggie Fox and Chris Wilson)