THE tragedy is so familiar. Mandy Brunskill's baby Liam was "a normal, healthy and bright little boy", then he was vaccinated against measles, mumps and rubella (MMR). The change was dramatic: he became listless and unresponsive. Liam deteriorated further and was later diagnosed as having severe autism.

All the families who have joined with the Brunskills to sue the makers of the vaccine have a similar story to tell. Their case is straightforward: the MMR jab is to blame for their children's autism.

Except that nothing is straightforward about this hugely contentious issue. It has pitted doctor against doctor, scientist against scientist and has left every parent confused as to the right thing to do for their child.

Whenever doubts are raised about the side-effects of MMR, the health establishment counters with the same arguments. Repeated studies have given the vaccine a clean bill of health. Autism naturally strikes at around the age when babies have the jab, the two are not connected. MMR is the safest way of protecting children against three life-threatening diseases.

The vaccine has undoubtedly been for the general good. No child has died of measles in Britain since it was introduced 13 years ago.

But that is not enough to quash parental fears about its safety. They are naturally worried about a process which exposes their very young child to a triple dose of germs.

Neither are GPs and nurses wholly convinced: a survey found that more than half had reservations about MMR.

The Department of Health's refusal to countenance giving the vaccine separately makes matters worse. Denied the choice, more and more parents are electing to opt out of MMR altogether.

This is an emotive issue. So the test case starting on Monday is very important.

All the evidence relating to MMR and autism will be aired in court. Then the judge will make a dispassionate ruling based on the facts available. That is what parents have been crying out for.

Updated: 11:02 Wednesday, December 05, 2001