Sooner or later, Jane O'Byrne is going to have to make her mind up about the MMR triple vaccine.

Like many parents of young children, Jane, from East Sussex, has strong doubts about the three-inone measles, mumps and rubella jab.

After reading stories about the triple vaccine, suggesting it may be linked to the brain disorder autism or inflammatory bowel disease, she is filled with doubts about giving the injection to her daughter Samantha.

"She is such a bright child, I would hate to think of giving her something that could take that away. I would never forgive myself if that happened," she says.

Dr Ian Holtby, a consultant in communicable disease, is baffled as to why so many caring, intelligent people are choosing to believe what, he says, are unsubstantiated scare stories about the triple vaccine.

"The history of MMR goes back 25 years and, around the world, 500 million shots have been given to children," says Dr Holtby. "Surely, if there was anything wrong with it, something would have come to light by now.

"International studies involving millions of children have failed to find any connection between the MMR vaccine and diseases such as autism or bowel disease.

"Often, autism becomes evident during the second year of life when children have their first MMR session so a lot of people will make the connection," he says.

Recent research shoots down criticism that the triple vaccine places strain on the developing immune system.

"A US study looked at the body's ability to handle all these antigens. By giving the triple vaccine, the body was still using less than one per cent of its capacity," the consultant adds.

He is also unimpressed by suggestions that parents should be won over by offering separate injections. "If we were to revert to three single vaccines, there would be a lot more injections and they wouldn't all get done.

"This would lead to more children exposed to diseases which have all but disappeared in the UK.

In the Third World, measles remains the biggest killer."

Such arguments fail to impress Paul Shattock, vice-president of the World Autism Organisation.

Mr Shattock has been researching the metabolical causes of autism for 20 years.

He is convinced there's a link between the MMR vaccine and autism, a condition which leaves young people suffering from profound communication difficulties.

"We realised there was a group of autistic children who didn't fit the pattern; they were more sociable than the others," says Mr Shattock, who admits he has no proof the sub-group are victims of MMR.

The "different" autistic cases began appearing in the early-Nineties, a few years after MMR began in 1988.

Mr Shattock has asked the Department of Health to hold an inquiry into the available evidence. So far, the answer has always been no.

He believes legal action taken by hundreds of parents who claim their children have been damaged by the MMR vaccine, will help to confirm his worst fears. "In my view, the evidence is very powerful," he says.