A study by scientists in the United States suggests a "strong association" between the three-in-one vaccine and autism.

They said the vaccine triggers an autoimmune response which they believe plays a role in the onset of autism.

There is a tremendous logical gap in this research

Professor Peter Lachmann, Cambridge University

But doctors in the UK have dismissed the study saying it provides no evidence of any link.

Dr Vijendra Singh and colleagues at Utah State University in Logan analysed blood samples from 125 autistic children and 92 children who did not have the developmental disorder.

Immune system

They found that the children with autism who had received the vaccine had raised levels of measles antibodies compared to those without the disorder.

Over 90% of the samples from these children were also positive for antibodies which the authors believe are involved in autism.

These antibodies attack the brain by targeting the basic building blocks of myelin, the insulating sheath that covers nerve fibres.

Dr Singh has maintained for a number of years that this process is one of the root causes of autism.

However, this theory is not widely shared. The paper's suggestion of a link between these antibodies, autism and the MMR vaccine have also been rejected.

Professor Peter Lachmann, Emeritus professor of immunology at Cambridge University, said: "There is no evidence of causality."

Speaking to BBC News Online, he added: "There is a tremendous logical gap in this research."

Research criticised

Dr Liz Miller, head of the immunisation division of the Public Health Laboratory Service, also criticised the study.

"There is no data in this paper that implicates MMR vaccine as a cause of autism nor that challenges the robust body of evidence on the safety of the vaccine".

In a statement, the PHLS added: "This claim by the authors that they have identified abnormal measles-mumps-rubella antibodies in autistic children is not substantiated by the data in the paper.

"No abnormal virus-specific antibodies have been demonstrated."

It continued: "The data that they show as evidence that this component is one particular antigen of the measles virus is not credible."

Vaccine warning

Professor Lachmann urged parents to have their children vaccinated.

"The evidence of the possibility of coming to any harm from the measles vaccine is so small that anyone who doesn't have their child vaccinated against measles is very foolish," he said.

There's a very, very strong case now for suspending MMR use while further investigations are carried out

Jonathan Harris, JABS

"Measles is not a trivial disease. If we were to have a measles outbreak the risks to children are very much higher."

However, campaigners said the study highlighted the need for more research.

David Potter, head of information and policy at the National Autistic Society, said: "The NAS would be keen to see further independent research to replicate these findings, which might provide a way forward in understanding and treating the condition."

Keith Lovett, of Autism Independent UK, said: "Parents have been suspecting this for many years now but research was needed in the area to back it up or put it to bed.

"It's certainly not going to go away until it's done properly. Proper trials are needed."

The study is the latest to look at the possible link between MMR vaccine and autism.

Figures show that the number of infants receiving the vaccine has fallen recently. Uptake fell from 76% to 70% between December last year and March. It rose to 72% in April.

The PHLS, Department of Health and British Medical Association have all consistently driven home the message that the vaccine is safe.

They have warned that low uptake of MMR could increase the risk of measles outbreaks.

But the anti-MMR pressure group JABS called on the government to reverse its position to only offer the three-in-one vaccine to parents.

Its spokesman Jonathan Harris said: "The evidence is building up tremendously. I really feel there's a very, very strong case now for suspending MMR use while further investigations are carried out."