"We have found no convincing evidence that MMR vaccination increases the risk of autism," Dr Liam Smeeth, of the London School of Hygiene and Tropical Medicine, said in a report in The Lancet medical journal.

"No significant association has been found in rigorous studies in a range of different settings."

Medical experts are worried that as the number of unprotected children rises more will become susceptible to infection and cases of the illness will increase.

The drop in vaccinations followed the release of a controversial report in 1998 that suggested a possible link. Ten doctors who co-authored the study have since said there is not enough evidence to draw that conclusion.

Smeeth and his colleagues compared the rate of MMR vaccinations of 1,294 children who later developed autism or other developmental disorder and 4,469 who did not.

They found that those with disorders were actually slightly less likely to have been vaccinated with MMR than those who developed normally.