The notion that the MMR vaccine can trigger autism should have ceased to be news long before this week’s widely reported study that shows it to be unfounded. From a scientific point of view, the hypothesis has never had much going for it.

The Andrew Wakefield paper that started the scare, published in The Lancet in 1998, reported only the anecdotal suspicions of a few parents who thought their children’s autism started when they were given MMR. It had no controls, it presented no evidence, and it has been so thoroughly discredited that the journal’s editor admits he should not have run it.

Wakefield and two colleagues are now defending allegations of serious professional misconduct from the General Medical Council.

Several epidemiological studies, which have compared the prevalence of autism with MMR vaccination rates in Britain and abroad, have found no association. Autism specialists, virologists and paediatricians have long spoken with one voice: the triple jab is as safe as any other vaccine.

Though the basis for alarm was flimsy, public concern has remained strong. Confidence in the vaccine collapsed after Wakefield’s claims, causing immunisation rates to fall to just 60 per cent in some areas. Measles and mumps have accordingly made a comeback: there were about 1,000 cases of measles last year, compared with about 100 annually before 2002, and cases of mumps now run into thousands instead of hundreds. Only recently has the immunisation programme started to recover.

There are lessons to be learnt from the saga. Health officials could have presented complex information about risk more clearly, and Tony Blair fed suspicion by refusing to say whether his son, Leo, had been vaccinated.

Parents should understand that, while a decision to vaccinate may seem to have risks, these are far outweighed by the real risks of leaving children unprotected. And journalists must learn to beware of mavericks with scary theories but few facts. The way much of the media stirred up the MMR panic did more damage than anybody besides Wakefield himself. But it is time to draw a line under the affair. The evidence is unambiguous, and this week’s study is important as it provides the missing piece.

The strongest card of the vaccine’s opponents has been their claim to have identified measles virus in the guts of some autistic children. This, if true, would support their hypothesis – though they’ve been loath to publish data, preferring announcements to newspapers. Strong doubt has been cast on the methods by which the virus has been found, but without detailed independent investigation of autistic children, the issue remained unsettled.

The Wakefield camp has long called for such a study, and it has now been done. The new research compared the blood of children with autism with that of typically developing children and those with other learning difficulties. All had had MMR.

If measles virus from the jab was causing autism, the effects should have been visible in the autistic group, through the presence of either persistent measles infection or measles antibodies in the blood. Yet neither was found: the blood of the autistic children looked identical to that of both control groups. The very study that the MMR critics wanted has given the vaccine a clean bill of health. It has shot their last fox.

Several junk medicine columns have discussed MMR over the past few years. It would be nice to think this will be the last one. Every ounce of evidence that has been assembled on the issue, now covering every possible approach, has reached the same conclusion: the vaccine does not cause autism. It is surely time for those who have claimed otherwise to apologise to the thousands of parents whose children have missed out on important health protection as a result.

Mark Henderson is Science Editor of The Times

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