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NARRATOR: In Britain today diseases that we had almost forgotten have returned. New outbreaks of measles have occurred and as a result, some children are already paying the price. Some say it's all down to this man. He is convinced that the combined Measles Mumps and Rubella vaccine could be damaging some of the children it's supposed to protect, that it could be causing autism. But the medical establishment says he is scaremongering. It claims that the MMR vaccination is safe. The result has been confusion, and many parents have shunned the MMR jab. Accusations have been made by both sides, questioning the motives of those involved, but what does the science show? Tonight, Horizon reveals new evidence that could provide the answer to the question so many parents have been asking: does MMR cause autism?

MIKE FITZPATRICK: Stop it. It's OK Jamsie. Shall we sing a song? [SINGING] No no no Jamsie - [SINGING] Hurray! Well James is eleven now and we've known he's been autistic since the age of two. He's quite severely autistic, he's got no language and he's got quite severe learning difficulties so he's on the extreme end of, the more severe end of the spectrum really. But he's a lovely boy and he's usually very happy, and very affectionate. But sometimes he gets very frustrated and I think perhaps because of his difficulty in communication, he - he will injure himself and then if you try and stop him, he'll sometimes get quite aggressive.

SUE McGOWAN: You press play. Good boy. Laurence is eleven now and we've known he's had autism since he was about three. Wind it up, wind it! If something goes wrong like this - it's broken. Well he's re-wound this this much that it's more or less had it, this video but he doesn't understand that. And as far as he's concerned, I'm not fixing it and because I haven't been able to help him with this video now, he's cleared off. He's gone downstairs because I, I'm no more use to him at the moment.

NARRATOR: Laurence and James both have autism. Autism is not one disease, it's thought to be a spectrum of disorders ranging widely in severity. But there are three features that are common to all children with autism - the so-called triad of impairments.

MIKE FITZPATRICK: One is a lack of the capacity for social engagement, forming social relationships, indeed really even recognising other people are human beings. He's not interested in other people. He's only interested in other people to get things for him really.

SUE McGOWAN: I think that's why they don't look at you. Laurence can't be bothered to make a lot of eye contact because he's interested in what he's doing. He doesn't want to know what you're doing.

NARRATOR: The second part of the triad is a problem with language, and in the most severe cases, no language at all.

MIKE FITZPATRICK: Good boy. He's never had any concept of language. I suppose the earliest manifestation of that sort of problem was you know not pointing things out to show people things.

NARRATOR: The third part of the triad is a lack of imagination.

SUE McGOWAN: He's not able to role play or anything like that. And I think you don't appreciate the imagination of a child until you have a child with no imagination.

NARRATOR: Autism is a lifelong condition for which there is no cure. And what frightens many parents is that increasing numbers of children are now being diagnosed with it. In Britain in the 1970s autism was found in one in two thousand children. Since then there has been an apparent ten-fold rise. Now at least one child in two hundred is diagnosed with an autistic spectrum disorder. Other countries have seen a similar rise. Science had no explanation for why autism should be increasing at such a rate. But one parent thought she knew the answer, and this would spark one of the biggest health crises of recent years. Rosemary Kessick has a sixteen year old son, William.

ROSEMARY KESSICK: I think the cat's sitting here forlornly wondering where he is. William's away at school.

NARRATOR: William now requires specialist residential care. But when he was a baby, things were very different.

ROSEMARY KESSICK: When William was born, he was wonderful. I had a great pregnancy, no problems at all. William was thriving and growing and jolly and bouncy and beautiful. William had an MMR at fifteen months and from then on, he for want of a better word, he disintegrated.

NARRATOR: The MMR jab combines three childhood vaccines against measles, mumps and rubella, into one injection which is first given at around twelve to eighteen months. It has virtually eradicated these diseases from the UK. Throughout the world it's saved hundreds of lives. But shortly after her son had the jab, Rosemary Kessick noticed a change in his behaviour.

ROSEMARY KESSICK: He stopped using the beginning of words, so "book" became "ook" and ball became "all". And then over the next twelve months those words just dissolved, and the very last word that he had was "juice". He developed a raging raging thirst and "juice" became "oose" and "oose" became "oo", and then it went completely.

NARRATOR: William now has no language and severe learning difficulties. And he also suffers from recurring bowel problems which started at the same time as his first signs of autism and just after the MMR. Rosemary was convinced the three things were connected.

ROSEMARY KESSICK: Within days after the vaccination, William was suffering from diarrhoea ten times a day which to me as a mother, and especially as William was my second child, was not normal. I knew he had a problem with the gut. I knew that everything had changed after the MMR but what I didn't know was what the link was.

NARRATOR: It was then that Rosemary came across the work of a doctor working at the Royal Free Hospital in London. His name was Andrew Wakefield. At the Defeat Autism Now conference in Washington, Andrew Wakefield is the guest of honour.

VOX POPS: I love the man for what he's done.

He should get a Nobel prize.

He's put everything on the line for our children.

A truly good man who bares the truth.

NARRATOR: He is now famous throughout the world as the man who proposed a link between autism and MMR. But back in the 1990s he knew little about autism.

Dr Wakefield is an expert in bowel diseases. He was working on a controversial theory that linked the single measles vaccine to a type of bowel disease called Crohn's, a theory that has never been substantiated. Wakefield's work didn't involve MMR but a different vaccine and a different disease. Still Rosemary believed he might provide the missing link: how the MMR could have caused her son's problems.

ROSEMARY KESSICK: I picked up the phone and phoned Dr Wakefield, and said to him I'm the mother of an autistic child and he's, he stopped me and said I don't know anything about autism, I'm a gastroenterologist. And I said well I have, I have a theory based on my own observations that the gut itself is the start point of my child's neurological problems. At the end of the conversation I said by the way, actually I think that the MMR has something to do with this because that's when my son changed. And he did not put the phone down on me.

NARRATOR: So Rosemary took William to the Royal Free Hospital, where Andrew Wakefield was based, to find out what had happened to him. There William was examined using a colonoscope, a flexible camera that allows the doctors to look inside his bowel. The colonoscope revealed that William's bowel was inflamed and scarred, and the damage wasn't quite like anything that Wakefield had seen before. It appeared to be a new form of bowel disease.

ANDREW WAKEFIELD (Royal Free Hospital, 1987-2001, interviewed in 1998): Children have a patchy inflammation of the colon and they also have great big swollen lymph glands in the terminal ileum which is the end of the small intestine. That combination, as we call it ileal hyperplasia, is the core of the gastrointestinal syndrome.

NARRATOR: Soon it became clear that William's case wasn't unique.

ROSEMARY KESSICK: I started receiving phone calls on the grapevine on the network. Parents had heard that there was somebody who had discovered something and increasingly parents were coming to me with the same story, the same thing has happened to their child in exactly the same way.

NARRATOR: So Rosemary told them about Dr Wakefield. And soon more and more parents were arriving at the Royal Free with similar stories of bowel disease and autism following the MMR jab.

ANDREW WAKEFIELD: Interestingly we set out to study ten children, we thought we might find inflammation perhaps in one or two based upon the history. We've now looked at forty children and thirty-nine of those have exactly the same findings.

NARRATOR: Dr Wakefield started trying to put the pieces together. Could the MMR jab be causing a strange new kind of bowel disease that was turning the children autistic? Then he started to investigate an even more disturbing possibility: could MMR be an explanation for the huge rise in autism? If so, the rise in different countries should match the introduction of MMR. Sure enough according to Dr Wakefield, the MMR vaccine had been introduced in the US in the mid-70s just as autism started to increase. Whilst in the UK, autism started rising in the late 80s, again just as the MMR vaccine was being introduced.

ROSEMARY KESSICK: The potential implications must have been a tremendous burden for Dr Wakefield because I guess at the time there was a decision to be made. Do we just bury it, do we pretend it's not existing or do we, do we forge ahead and identify what's really happening?

NARRATOR: If MMR really was the cause of an epidemic of autism, this was a public health disaster of huge significance. It would mean thousands of babies were being damaged by the vaccine. This became a central claim of the anti-MMR campaign.

ROSEMARY KESSICK: We are facing an autism epidemic and if it isn't taken seriously now, when it does come home to roost, the cost to the nation is going to be absolutely unbearable.

NARRATOR: But the question remained: how could a vaccination designed to protect children be causing autism? Wakefield believed he had an answer. When a child is vaccinated, a small amount of virus is injected into the body. Because the virus has been weakened, the body's immune system easily defeats it leaving the child protected. But Wakefield suspected that by giving three different viruses, the immune system was being overwhelmed. Instead of being defeated, the measles virus from the vaccine remains in the body. Wakefield's theory was that the measles virus causes a persistent infection of the gut, leading to bowel disease. This bowel disease stops the gut from digesting food properly, creating toxic chemicals called opioids. These opioids then enter the blood stream and make their way to the brain where they damage the developing brain, causing autism. It was a bold and controversial theory. Wakefield decided to write a paper outlining his theory and describing William and eleven other cases. He succeeded in getting it published in one of the world's leading medical journals, The Lancet. The paper described the new form of bowel disease associated with autism. On its own, this would have attracted little attention outside the medical community but the second half of the paper was explosive. Even though, as Wakefield himself admitted, there was no proof that MMR was the cause of autism, the paper raised that possibility. As well as having an autistic son, Mike Fitzpatrick is also a GP so he soon became aware of Wakefield's research.

MIKE FITZPATRICK: When I first heard about the Lancet paper alleging a link between MMR and autism, I was concerned as a GP because here we were doing baby clinics where we were giving the MMR routinely. I was even more concerned as a parent of an autistic child. So I made it my business to check it out very thoroughly. Well when I got to read the Lancet paper, I must say I was really shocked because it was such an insubstantial and speculative paper.

NARRATOR: According to his critics, not a single stage of the mechanism linking MMR to autism was supported by scientific evidence. There was no evidence that MMR could overload the immune system. No evidence that the measles virus had infected the gut. No evidence that this infection had caused bowel disease, and no evidence that the bowel disease was causing autism.

MIKE FITZPATRICK: There were four speculative stages in the theory, each of which was highly speculative.

NARRATOR: But what really propelled the theory into the headlines was a press conference given to launch the paper. There Andrew Wakefield made a controversial suggestion.

ANDREW WAKEFIELD: There is sufficient anxiety in my own mind about the safety of the MMR vaccination and I think that it should be suspended in favour of the single vaccine.

NARRATOR: Wakefield was suggesting that instead of the combined MMR, children should be given measles, mumps and rubella vaccines separately. The result was a media storm.

TV NEWS: Controversy over the MMR jab - The vaccine has been linked with autism. Scientists at the Royal Free Hospital in North London say they found cases of a bowel condition associated with autism soon after the MMR injection. The scientists want the government to look again at how we vaccinate.

NARRATOR: And from that day on, MMR vaccination rates started to fall.

NEWS: This clinic in south London has been inundated with parents demanding. It's getting five hundred calls a day.

NARRATOR: Parents began demanding the single vaccines just as Dr Wakefield had recommended. According to Wakefield, this was the perfect solution: the protection of the vaccines without the risks of MMR. But others disagreed.

Dr LIZ MILLER (Health Protection Agency): That suggestion in practice would result in many many children being unprotected. It's six injections. The likelihood that many children would not come back for the six injections I think is very high. It was an irresponsible suggestion.

NARRATOR: Perhaps the biggest fear is the impact on rubella vaccination. Rubella, or German measles, causes only a mild disease in children so it's possible that with single vaccines available many parents wouldn't bother giving their babies the rubella vaccination. But rubella is dangerous for pregnant women. The fear was that rubella would be passed from unvaccinated children to expectant mothers, with devastating consequences. This is exactly what happened before MMR.

DR LIZ MILLER: Whenever there was a rubella outbreak amongst children, women got rubella from their own children. In some cases it was diagnosed in pregnancy, resulting in a rubella termination for which in the bad years there would be eight hundred a year. Those women who didn't get diagnosed in pregnancy would continue with their pregnancy unaware that they'd been infected and then give birth to a child with congenital rubella syndrome.

NARRATOR: Camilla suffers from congenital rubella syndrome and, as a result, she was born deaf and blind. With the introduction of MMR such cases have virtually disappeared but the fear was that offering the choice of single vaccines would mean more cases like Camilla. So for the authorities, there was no easy way out. Introducing single vaccines could put children at risk. But if Wakefield was right, this could be a price worth paying to prevent an epidemic of autism. The vital question was: could Wakefield get the evidence to back up his theory? A key piece of evidence in Wakefield's paper was the timing. In all twelve cases that he described, symptoms had appeared within a couple of months of receiving the MMR. For Rosemary Kessick, this was clear evidence of a link.

ROSEMARY KESSICK: It was quite clear to us as a family that William was perfectly normal, perfectly alright when he was born and right up until he had the MMR.

NARRATOR: But to scientists, such evidence has to be taken cautiously.

Prof STEPHEN SENN (Statistician): I think that there's an inevitable tendency to mistake subsequence for consequence, that is to assume that because one particular event follows another, that therefore the preceding event caused it.

NARRATOR: The problem is MMR is usually given between twelve and eighteen months which is also when autism is often first spotted. So you will inevitably get the two events occurring together just by chance. It's even possible to calculate how often this will happen.

SENN: There are about seven hundred thousand births in the UK every year, and about two out of every thousand will develop signs of autism at some time during their life, so that gives us about 1,400 such children every year. If we now ask the question, well, what proportion of those would develop autism during the period of interest which is one year to eighteen months, then the answer is slightly in excess of fifty percent. So we can say of the 1,400, let's say about 800 would develop signs of autism in that particular period. If we now ask the question well of the 800 children, how many will have received the MMR vaccine, about eighty percent let's say, that brings us down to 600 children, so 600 children in a six month period so we're talking about in any given month, one sixth of 600, 100 children would develop signs of autism within one month of having received the MMR. But now imagine that you're a parent of a child, who has had the MMR vaccine. You're bound to associate one with the other and yet the statistics suggest that simply by chance even if there is no causal link a hundred such cases will appear every year.

NARRATOR: But Wakefield and his supporters claimed it wasn't just a matter of timing. They believed that MMR was linked to a very particular kind of autism.

ROSEMARY KESSICK: Our children are autistic in a different way from autism that was originally postulated, was originally talked about. Our children are regressive autistic.

NARRATOR: The conventional theory was that autism is present from birth but the families who came to see Dr Wakefield seemed to have a different story. Their children seemed to be normal until the MMR.

SUE McGOWAN: It's quite difficult to look at the ones when he was really young. These sort of photographs, before you knew that anything was wrong. He used to like visiting, sitting with his grandma and he had little friends. When he was about two and a half we realised that there was something wrong but we didn't know how serious it was going to get.

NARRATOR: Like Rosemary Kessick, Sue believes that her son was developing completely normally and then his development stopped. He regressed.

SUE McGOWAN: This is Laurence when he was about nine years old. He'd gone from a chubby healthy baby like this, to a child thin and ill, cold, weak. We got to the stage where we, we weren't able to take him out for a walk or anything. He'd basically turned his face to the wall in the end.

NARRATOR: Many campaigners claimed that the emergence of this regressive form of autism proved that something was damaging the children. But is there really a new regressive form of autism? If anyone would have noticed a change in the condition, it would be Lorna Wing. In the 1940s Lorna Wing trained as an adult psychiatrist but her career changed direction when her own child was diagnosed with autism. She became one of the first researchers in the country to study the condition and is now respected by both parents and scientists, and over her long career she has come across many reports of regression.

LORNA WING (National Autistic Society): Autism can begin any time up to the age of three so this notion of a child apparently developing normally and then becoming autistic is certainly not new, not new at all.

NARRATOR: This footage from the 1960s shows a happy normally developing toddler. This child went on to develop severe autism. So regression existed long before MMR and a recent study has shown that it occurs just as often in children who haven't had MMR.

LORNA WING: In my experience I haven't seen any increase in the number of people who say that their child became autistic after developing normally.

NARRATOR: So far there was no conclusive evidence that MMR had caused a single case of autism, but that didn't stop the decline in public confidence in the vaccine. As increasing numbers of parents shunned the MMR vaccine, diseases which in Britain had almost been consigned to history have returned. Cases of measles and mumps have started to rise, and these diseases have already claimed their first victims.

KAREN PETIT: Most people think of measles as a rash and a week off of school. It's not quite that simple. It would be nice if it was just a week off school and a rash but - you know -

MATTHEW: It's not. More complicated.

KAREN PETIT: Very complicated, yeah.

NARRATOR: When he was two years old, Matthew had a kidney transplant. It saved his life but it left his immune system weakened, putting him at particular risk from childhood diseases. And in 2002 Matthew discovered just what measles can do.

KAREN PETIT: Matthew got up at quarter to five one morning to go to the toilet. On the way back he just collapsed in the hallway. I went out to see what was the matter and he was just having a fit. He was just laying on his side and all his body was shaking, he just wasn't responding to anything.

MATTHEW: Nightmare.

NARRATOR: Matthew was rushed to hospital where his condition deteriorated.

KAREN PETIT: He was just getting worse in front of our eyes. He'd lost the use of his hands, his legs and then on the Sunday his eye sight went. He just couldn't see anything.

NARRATOR: After two weeks of investigation, doctors discovered what was causing the damage. It was measles.

KAREN PETIT: They called it measles encephalitis, it just swelled his brain up and affected all the left hand side of his body.

NARRATOR: Matthew has been left with brain damage from which he may never fully recover.

KAREN PETIT: Matthew can no longer walk. He can't use his left leg and his left arm. He's just like jelly. It's affected his hearing and he's been registered partially sighted. His main hobby was reading. Obviously now he's lost his sight, he can't read.

Chapter 4, Confusion in the Marketplace.

NARRATOR: With his weakened immune system, Matthew couldn't have the MMR jab himself so his health had relied on other children being immunised; but the area of London where he lived had one of the lowest vaccination rates in the country.

KAREN PETIT: The only protection that the immuno-suppressed children have is that the uptake of the MMR jab is kept to a high because once they've caught a disease such as measles -

MATTHEW: That's it.

KAREN PETIT: It's sort of - it has just ruined Matthew's life really.

NARRATOR: It isn't only children like Matthew who are at risk.

DR LIZ MILLER: If this continues for a number of years, we will undoubtedly have the return of epidemic measles and with that, there will be children who will die and children who will be brain damaged. This isn't a hypothetical risk.

NARRATOR: The authorities were facing a real problem. Dangerous diseases were on the rise, while MMR uptake fell further. To turn the tide, they needed a conclusive answer to the questions over MMR so they turned to a method they hoped would provide that answer: epidemiology.

STEPHEN SENN: Epidemiology is the study of the health of populations. Huge populations. And really requires measuring events that happen to lots of people in order to try and work out what are the causes of ill health.

NARRATOR: Dr Wakefield had claimed that the rise of autism had started at about the time MMR was introduced, so epidemiologists looked more closely to see if the data really matched up. The story turned out to be much more complicated.

DR LIZ MILLER: The rise occurred before MMR was introduced. It continued after MMR was introduced. Even though the uptake rate of MMR was constant, the rates at which autism was being diagnosed were increasing.

NARRATOR: And in Japan, the MMR vaccine was withdrawn in 1993. But a recent study has shown that autism rates there have still risen. So the evidence suggests that MMR wasn't responsible for the epidemic, but that still didn't prove that it was safe. To really find out whether MMR increases the risk of autism, scientists needed a way of comparing children who did have the vaccine with children who didn't, and in one country just such a study was possible. In Denmark, every child is given a unique social security number on the day they are born. This number is used to record every medical event in their history so researchers pulled out the data for every child in Denmark born between 1991 and 1998, more than half a million children.

Although the majority of Danish children do receive the vaccine, there were almost one hundred thousand children who hadn't, so scientists could compare the rate of autism in those two groups. And they found that the rate was the same, whether they'd had MMR or not.

DR LIZ MILLER: There was no difference. In fact, there was a slightly higher risk in the unvaccinated group. It wasn't statistically significant but there was absolutely no evidence of an increased risk in those that had been vaccinated.

NARRATOR: Opponents of MMR have claimed that there might be flaws in the Danish analysis but there have been more than a dozen epidemiological studies using different methods in different countries, and overwhelmingly they have found no link between MMR and autism. To the scientific world, the statistics confirmed that MMR is safe.

DR LIZ MILLER: It's absolutely clear that if there has been a large rise in autism, it's got absolutely nothing to do with the vaccine.

MIKE FITZPATRICK: It's been given in eighty countries for thirty years, in millions of doses and if it did cause a significant adverse reaction, it would have been picked up somewhere by now.

DR LIZ MILLER: You know I'm at a loss to - what more can be done. There is no epidemiological evidence to suggest that there is a link between the two.

MIKE FITZPATRICK: As far as anything you can say is safe, MMR is safe.

NARRATOR: The epidemiology had shown that the huge rise in autism had not been caused by MMR. But if MMR wasn't responsible for the rise, then what was? Many experts believe that the increase in numbers may be largely down to better diagnosis, that there have always been a similar number of autistic people but they never got diagnosed.

LORNA WING: Now I can think back to when I was working in an old-fashioned mental hospital as a psychiatrist for adults, it's absolutely clear to me that a number of the people I knew then who were chronically ill and had lived a long time in the hospital, were certainly autistic people grown up.

NARRATOR: The epidemiology gave MMR the all-clear. But opponents of the MMR vaccine are still not convinced.

ROSEMARY KESSICK: The only evidence which I've seen cited is epidemiological. Now to me that's statistics. Now statistics either turn you on or they don't. I don't, I don't have time for statistics when I see a sick child in front of me.

NARRATOR: Although the epidemiology showed that MMR couldn't be a risk for the vast majority of children, Wakefield and his supporters now believed that there might be a small group of children that had been damaged by MMR. If this so-called sub-set was small enough, it wouldn't be detectible by epidemiology; and Wakefield claimed this wasn't just a theory. He had scientific evidence to back it up. The clue lay in the new form of bowel disease that Wakefield had discovered.

SUE McGOWAN: It seems not too bad at the moment.

NARRATOR: Sue McGowan believes that her son is suffering from this bowel disease.

SUE McGOWAN: It's just here and it will just, it will just swell like this here, and then you know he'll ask me to rub it like this.

NARRATOR: At one point, Laurence virtually stopped eating and his weight dropped to two stone eight, the typical weight of a child half his age.

SUE McGOWAN: I think it's a gut problem and that I think is affecting his mental condition because something sends him berserk every so often and it always happens just after he's eaten.

NARRATOR: Sue believes that the pain from his gut problems leads to a worsening of his autistic behaviour.

SUE McGOWAN: Because of the nature of his problems, we don't know what kind of pain he's in. Anybody who's had a stomach ache or diarrhoea, imagine having that all the time.

NARRATOR: For Wakefield, the bowel disease that children like Laurence are suffering from is a key symptom of this vulnerable sub-set. But in fact, bowel problems are common in children with neurological conditions so most gastroenterologists have tended to see such symptoms as unsurprising.

Prof SANDHU (Bristol Royal Hospital for Children): Neurologically abnormal children, about fifty percent of them, have constipation, some diarrhoea, bloating, abdominal pain. So to me that's not a surprise.

NARRATOR: If anything, Professor Sandhu believes it's not the bowel disease that is causing autism, it's the autism that's causing the bowel problems. The reason is that the brain and the digestive system are very closely linked.

SANDHU: After the brain, the gut has the largest number of nerves in it so it's very influenced by feelings in the brain, as we know, you know you're going for an interview and you're running to the loo so the gut/brain axis works but it's mostly that way round, not the other way round.

NARRATOR: But Wakefield claims that sceptics like Professor Sandhu are missing the point. He says that children such as William and Laurence don't just have bowel problems. They have a specific new form of bowel disease that is particularly associated with autism. Using a colonoscope, this is visible as a distinctive pattern of damage in the gut. The man who performed the original investigations was Simon Murch.

SIMON MURCH (Royal Free Hospital, 1995-2004): The first two or three children had really very striking changes. One had ulceration in the bottom of the small bowel, what's called the terminal ilium. Now that was of sufficient severity that we actually thought this was Crohns disease.

ANDREW WAKEFIELD (Dr Andrew Wakefield, Interview on Â鶹Éç Panorama 2002): We've now scoped over two hundred children or in other words performed this invasive procedure on two hundred children to investigate the intestinal tract, and find that there is a remarkably consistent disease.

NARRATOR: Although Wakefield's claims are supported by a small number of scientists, the majority of gastroenterologists are still sceptical about the existence of the new condition.

PROF SANDHU: Certainly I've talked to you know the majority of my colleagues around the UK, in UK and north America and they pretty well agree with us. I mean where perhaps we haven't been very good is actually saying this to the public, that this is a whole lot of nonsense.

NARRATOR: But Wakefield responded that he had a second key piece of evidence that showed that a sub-set of children could have been damaged by MMR. He claimed to have found the measles virus in their bodies. Wakefield's theory was that the measles virus in the vaccine was causing a persistent infection so it should be possible to find traces of the virus in the child's body. His own laboratory had searched for the virus but without success. But then he met someone who was to take his research to a new stage. John O'Leary is an expert at detecting viruses, even when there's only a small amount of the virus to find. He uses a technique called PCR which can make copies of the genetic code inside a virus, turning a single copy into billions. So with PCR, you can detect even a single virus particle. Wakefield sent O'Leary small samples of bowel tissue that he'd taken during the examination of the children. O'Leary tested these samples for the presence of the measles virus and what he found would re-ignite the MMR controversy once more.

JOHN O'LEARY (Trinity College Dublin, Interview on Â鶹Éç Panorama 2002): We've identified a persistent measles virus infection in the guts of these children which is statistically significant as compared to normal controls.

NARRATOR: O'Leary claimed to have found the measles virus in 82% of the samples from the autistic children examined by Dr Wakefield. Then he went further and claimed to have found the virus in the blood of autistic children.

ROSEMARY KESSICK: What O'Leary had found was fragments of the measles virus in both the blood and gut samples. Now there was no reason why the measles virus should be there and where did it come from in vaccinated children? It had to have come from the vaccination.

ANDREW WAKEFIELD: It tells us that in children whose only recorded exposure to the virus has been as the vaccine, the vaccine or the virus is still there in their intestine often many years later.

NARRATOR: O'Leary's research propelled the MMR controversy into the news once more. Headlines presented it as proof of a link. But again many scientists were not convinced by O'Leary's work.

PHILIP MINOR (Virologist): We had been waiting for really some time to see when this material was going to come out and appear in a peer-reviewed journal and so on, and it was a big disappointment frankly. From a virological point of view, almost impossible to assess.

NARRATOR: The problem is that PCR can sometimes be too good. Its incredible power to copy a single piece of genetic material means that the tiniest bit of contamination can make the results worthless. According to his critics, O'Leary's paper didn't have enough detail to show whether his methods were reliable or not.

PHILIP MINOR: Because it's so sensitive, anything that's a contaminant that creeps in from in this case a measles sequence either in the lab or in the sample that you're looking at or floating in the air or whatever, can actually give you a very misleading result.

NARRATOR: And so the two sides were deadlocked. The anti-MMR campaign believed that they had strong clinical evidence: the new bowel disease and the presence of the measles virus, to back up their claims. But the medical establishment dismissed their case, preferring to rely on epidemiology. And for years, little independent clinical research into these claims was funded - to the anger of many parents.

ROSEMARY KESSICK: It needs clinical scientific research. Forget the epidemiology. Look at the children, look at the samples, look at the samples down a microscope. Keep the science.

NARRATOR: The lack of such research has fuelled suspicion that the government simply wasn't taking people's concerns seriously. But now at last the deadlock is being broken. New clinical research is going on to answer the questions. Is there a sub-set of autistic children with a new form of bowel disease? And can the measles virus be found in the blood of autistic children?

TIMOTHY BUIE (Massachusetts General Hospital): All I want to do, that's it. I'm going to quit. Don't quit if that's what you want to do!

NARRATOR: Timothy Buie is a paediatric gastroenterologist in Boston. What makes him unique is that he works in a clinic that specialises in the care of children with autism and related disorders. Like Dr Wakefield, he has found that many of these children do have real bowel problems that are worthy of investigation, and in some cases, the parents blame their child's problems on MMR.

FEMALE: She got the MMR shot at about eighteen months old, about twenty months, twenty-two months it was just - everything started dropping away, it was just like one day all of a sudden a wall went down. She stopped responding, she stopped talking, she stopped looking at us. It was scary, it was like I lost my child.

BUIE: Parents are not being reassured by an answer that we think this is OK, we know this is OK. Epidemiologically this looks OK. Parents are not confident with that answer yet. We need to do the work to look for the answers and try to confirm or refute the finding.

NARRATOR: The question is: do these children have a unique pattern of damage caused by a new form of bowel disease, as claimed by Andrew Wakefield? Answering that requires colonoscopy.

BUIE: So this is a colonoscope and it has camera technology that really allows us to look down with light into the gut. And literally winding through the colon is like driving a grand prix. We try to be very careful to come around corners. Wheels on the top of the scope let me turn. I can use my body to turn and reposition the scope. I think people who are very good endoscopists are quite artistic. They look like they're doing tai-chi at times. What did he eat? We're going to get a culture of seeds here. I do not know what he ate! Look at that. One of the biggest challenges I think sometimes to get into the end part of the small intestine because it's sort of, it's a very sharp turn.

NARRATOR: Finally Dr Buie manoeuvres into the small intestine. Here he finds prominent nodules of lymph tissue. Enlarged lymph nodes in the gut are one of the features associated with the new disease.

BUIE: And you can actually see them beautifully illustrated in this child. He's got an area on the small bowel that is on one side of the bowel, is very smooth, and on the other side of the bowel it's very lumpy and bumpy and nodular.

NARRATOR: But this child isn't autistic. He's developmentally completely normal.

BUIE: Most paediatric gastroenterologists would say that they see this very frequently. They see it in most children, especially children in this age under age seven or eight.

NARRATOR: His research is still ongoing but despite having performed colonoscopies on hundreds of children, both with and without autism, Dr Buie has so far seen nothing that convinces him that autistic children have a new or distinctive form of bowel disease.

BUIE: I'm not sure that I can support at this point that the findings of colitis are novel or different than other conditions that we know.

NARRATOR: Buie's work casts doubt on one plank of the Wakefield hypothesis, that there's a new form of bowel disease. But perhaps the most crucial question is whether the measles virus really is persisting in the bodies of autistic children. But now that question too has been investigated. Here at Guys Hospital in London, scientists have been studying a large group of a hundred autistic children. Although taking bowel sample was considered too invasive, they did examine blood samples from the autistic children, as O'Leary had done. The researchers were looking for traces of the measles virus in the blood samples and in samples from other children the same age. If the virus was found more often in the autistic children, it would be evidence of a link. The samples were analysed in several of the leading laboratories in the country, including the National Institute of Biological Standards and Control, and the Health Protection Agency. They used the most sensitive methods available. And they found that 99% of the samples did not contain any trace of the measles virus. Crucially, there was no difference between the autistic and the non-autistic children. Although this research has not yet been published, Horizon has learned that it has found nothing to show any link between MMR and autism. When epidemiology found no evidence of a risk from MMR, the opponents of the vaccine replied that the evidence was there in the children if only someone would look, but these scientific studies of children with autism have also found no link with MMR. Wakefield claims that there is other ongoing research that will support his theory. But the overwhelming majority of scientists are convinced that the issue is settled.

MURCH: I think the uncertainty that was raised has been ruled out now by a huge number of studies. The evidence is really very clear now, completely clear that MMR is not the cause of autism.

NARRATOR: For some parents it may never be possible to accept that MMR isn't the cause of their child's condition.

ROSEMARY KESSICK: I can't see how any study could prove that the MMR hasn't caused the regressive autism that we're seeing in the children, not with the stack of evidence that we have. We do have a stack of evidence.

Q: As far as you're concerned, the case is 100% proven?

ROSEMARY KESSICK: Yes.

NARRATOR: But for most parents with an autistic child, there will be huge relief in knowing that nothing they did caused their child's condition.

MIKE FITZPATRICK: You know there were all these theories in the past that parents in some way were to blame for their children becoming autistic and there's now the modern version of that is that parents are to blame for giving their children MMR. If only they hadn't given them the MMR, they wouldn't be autistic.

Do you want some drink, Jamsie?

I think that's had a very baleful effect on parents of autistic children.

You're tired at the moment aren't you Jamsie?

NARRATOR: And if the number of measles mumps and rubella cases rise, other children may pay the price for the lack of confidence in MMR.

FITZPATRICK SINGING

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