Dr Andrew Wakefield is a man under pressure. Last week he published research indicating a possible link between the MMR vaccination against measles, mumps and rubella and inflammatory bowel disease and autism. It is a finding that will have chimed with parents' deepest fears about the safety of exposing babies' developing immune systems to potentially toxic drugs. But it also threatens to destabilise carefully nurtured vaccination programmes which are acknowledged to have saved millions of lives worldwide. That is a heavy responsibility, as Dr Wakefield knows. "I have thought about this every night for the last ten years. My children say 'Why do you do what you do, Daddy?' and I do not know what to say to them. It is a moral issue for me."
His story begins in Canada in the late 1980s, where he had been working as a transplant surgeon. He became dissatisfied with chopping out pieces of diseased bowel and wanted to know what triggered the disease process in the first place. One freezing night, drinking a pint of Guinness in a bar, he had an inspiration. What if inflammatory bowel disease was not a bowel disease at all, caused by bacteria in the gut, but a vascular disease caused by damage to the blood supply to the gut wall?
He returned to England "in something of a crisis" and set to work at the Royal Free Hospital, north London, to test his hypothesis. With his close colleague, Professor Roy Pounder, who has stood by him throughout their decade-long association, he demonstrated that the blood supply was indeed broken down by an insidious destructive process. They published the first of a series of papers in The Lancet in 1989, although their theory remains controversial.
The next question was what caused the blood vessels to break down. At the time there was a lot of interest in viruses in blood vessels. "I sat down with two volumes of a virology textbook and worked through it. I got to measles virus and it described how it gets into the gut, causing ulcers and inflammation. You could have been reading an account of Crohn's disease [inflammatory bowel disorder]. It was very exciting."
That was in 1990 and the pair started looking for measles virus in bowel tissue taken from patients with Crohn's disease. They have been looking ever since.
In a paper in 1994 they claimed to have found it and said Crohn's disease was three times more common in people who had had measles vaccination. That study triggered a new rush of parents to Dr Wakefield's clinic claiming their children had developed symptoms of autism and bowel disorders shortly after MMR vaccination. The result was last week's paper.
Morality and science make uneasy bedfellows. When Dr Wakefield speaks of morality he refers to his duty to his patients. "We get these parents ringing up every day. They say 'My child has autism and bowel problems and we believe they are linked'. You have to do something for them. These are the people to whom we are answerable."
He admits this makes life difficult for public-health doctors whose corresponding duty is to care for populations, but it can't be helped. His patients come first.
Dr Wakefield, a reader in experimental gastro-enterology, is not a crank. His research has been published in The Lancet, after being submitted to expert peer review. He has 12 co-authors on his latest paper and is regularly invited to speak at international meetings on gastro-enterology.
Yet he has been vilified and his research has been attacked as flawed and inadequate. Even The Lancet was nervous about it, commissioning a highly sceptical commentary and deliberately omitting it from its usual press release "to avoid being alarmist", according to a spokeswoman.
The Government moved swiftly to reassure parents, while the research team, from the Royal Free Hospital, emphasised that they remained in favour of immunisation.
One of Dr Wakefield's co-authors confided last week that he would prefer to work on the link between bowel disease and autism and leave aside the emotive question of the link with MMR for the sake of a quieter life.
That remark drew a stinging response from Dr Wakefield. "If they are uncomfortable they should look for a quieter life elsewhere. I can't do that."
The history of scientific advance is littered with individuals who held out against major political and commercial interests. Think of smoking and cancer. But they are hugely outnumbered by those who believed they were on to something and whose hypotheses later died. Indeed, the British Medical Journal declared Dr Wakefield's hypothesis dead in a an editorial published only six weeks ago.
If he is right about MMR, governments worldwide will have to rethink their vaccination policies, manufacturers will face a raft of compensation claims and hundreds of patients who have harboured suspicions about the safety of vaccinating young babies will feel vindicated.
If he is wrong, the consequences could be still more serious if vaccination rates fall and measles cases start to rise.