The number of cases levelled off in the early 1990s after rising through the 1980s. However, there is evidence of more parents blaming the triple measles, mumps and rubella vaccine since August 1997, when the first claims were made of a link between the jab and bowel diseases and a new form of autism.

A team led by Brent Taylor, of the Royal Free and University College medical school, London, followed up its previous research in areas of north-east London which had suggested increases in cases.

It reports, in the journal Archives of Disease in Childhood, that incidence appeared to have reached a plateau between 1992 and 1996 at 45 to 50 new cases a year, or 2.6 cases per 1,000 live births. "This levelling off, together with the reducing age at diagnosis, suggests the earlier recorded rise in prevalence was not a real increase but was likely due to factors such as increased recognition ... and better recording systems."