In a letter published this week in The Lancet medical journal, Dr. Simon Murch warned the proportion of toddlers getting the vaccine, known as MMR, has dropped so low in Britain that major measles epidemics are likely this winter.
Measles has resurfaced in Britain over the last few years in areas where MMR use has dipped; more children are getting infected every year.
The World Health Organization said Ireland, Spain, Italy, Germany and Switzerland have also had recent outbreaks of measles and that declining MMR vaccination is likely a contributing factor.
"Although this situation reflects in part a broader mistrust of official pronouncements, and has been fueled by media campaigning, it is founded on the misinformed perception that there is ongoing scientific uncertainty," said Murch, a pediatric gastroenterologist at the Royal Free Hospital in London.
"There is now unequivocal evidence that MMR is not a risk factor for autism - this statement is not spin or medical conspiracy, but reflects an unprecedented volume of medical study on a worldwide basis," Murch said.
There has been no significant drop in MMR vaccination rates in the United States over the last eight years, according to the U.S. Centers for Disease Control and Prevention.
Fears over the MMR vaccine intensified in Britain in 1998 after a study that Murch and others conducted raised the possibility of a connection between the vaccine and developmental problems in 12 children with bowel ailments. The study was done about eight years after the children had been vaccinated and involved parents remembering whether the autism symptoms occurred around the same time as the vaccination.
Immunization rates in Britain and other countries began to fall after the 1998 study. The national rate in Britain has slipped from 91.7 percent in 1997 to 78.9 percent in June of this year, well below the 90-95 percent specialists say is needed to prevent measles returning.
Several authoritative groups, including the World Health Organization, the U.S. Institute of Medicine, and Britain's Medical Research Council, have reviewed evidence investigating a possible link between the vaccine and autism and all came to the conclusion that the two are not connected.
However, fears have lingered. In some areas of England, the MMR vaccination rate among 2-year-olds is 61 percent, which Murch says means measles will almost certainly take root again in Britain. And the near elimination of congenital rubella syndrome - which can result in abortions or severe birth defects - will surely reverse, he said.
Murch said he was prompted to write the letter by the increasingly urgent measles and rubella threat and the fact that fears have not dissipated in some areas, leading to further declines in MMR vaccination.
"We've seen well over 300 children with autism, and even in cases where there is clearly a genetic cause of autism or when there were problems manifesting in the first year, parents are still fixated on MMR," he said. "It's a natural human reaction. They want something to blame for such a tragic event."
The risk from the combined vaccine, if there is any, is "being grossly overestimated," Murch said.
On the other hand, unvaccinated children pose a deadly risk to children whose immune systems are vulnerable, such as those recovering from cancer treatment, he said.
By Emma Ross