The study, published in the New England Journal of Medicine, examined the medical records of more than half a million children born in Denmark over eight years. Of the 537,303 children born between January 1991 and December 1998, 440,655 (82%) were given the MMR vaccine, usually at around the age of 15 months.

Researchers found that 758 children had been diagnosed either with autism or with autistic-spectrum disorders, but that the vaccinated children were no more likely to have such a diagnosis than those who had not been vaccinated.

The authors, Kreesten Meldgaard Madsen from the Danish Epidemiology Science Centre in Aarhus and colleagues, conclude that "this study provides strong evidence against the hypothesis that MMR vaccination causes autism".

The paper found not only that the risk of autism was similar in vaccinated and unvaccinated children, but also that there was no sudden surge of cases just after children received their MMR, or at any other time.

One of the main reasons for public concern, the authors write, is that cases of autism have appeared to rise following the introduction of the MMR vaccine for the whole population. In Denmark, however, they say the rise in autism occurred from the mid to late 1990s, well after introduction of the vaccine.

The Department of Health said it "welcomes this latest evidence which finds no causal link between MMR and autism" and will be hoping it may reassure some of the parents who have abstained from giving their children the triple vaccine.

Senior doctors in Britain say there is no evidence for separating out the three vaccines. In fact, said Adam Finn, a vaccines expert from the University of Bristol medical school, combinations of vaccines have been used for decades.

The DTP - diphtheria, tetanus and pertussis (whooping cough) - combination has been used since the 1950s and even the polio vaccine is a combination of three different strains. It has to be given in three separate doses over three months so that the strains do not interfere with each other.

Multiple vaccines were not only the past, said Professor Finn, but the future. "A single, one-dose vaccine that you give to all babies at birth by mouth that protects them against all childhood illnesses - that is the goal. We are working to try to combine them wherever possible."

The immune system was able to deal with much greater challenges than a few vaccines, he said. A study in the American journal Paediatrics in January said a baby's immune system could cope with as many as 1,000 vaccines at once, if it were necessary.

Ironically, Prof Finn said, the MMR had virtually no side-effects, whereas the polio vaccine, which parents are happy with, was responsible for the only - if very rare - occurrences of polio in Britain.

Because there was a chance that one child a year at most might die or be damaged as a result, the government would probably substitute an injected version of inactive polio virus for the oral live virus in the near future. But an injection which was safer than the oral dose might become a cause of concern for parents, particularly if it was added in with the DTP, which now contained the Hib vaccine.

David Ellerman, NHS immunisation coordinator for south London, said on Radio 4's Today programme that multiple vaccinations in a single injection were kinder to the child.

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