MMR & Autism

Is there any evidence that the MMR vaccine causes autism?

The NAS has consistently recommended that parents discuss issues and concerns relating to vaccination with the relevant health professionals. The NAS believes continued efforts are required on the part of the Chief Medical Officer, supported by further authoritative research, to put these matters beyond doubt and so allay any remaining public concern.

Whilst we are aware that there are a number of parents who feel that their children's autism has been caused in this way, there is to the best of our knowledge no conclusive scientific evidence to prove this at present.

The interest in a possible link was first raised by the research of Dr Andrew Wakefield's team at the Royal Free Hospital in February 1998 (1). This noted that in the twelve children seen by the research team, the symptoms of their developmental disorder became apparent within six days of their receiving the MMR vaccine. This was a very small-scale study and it concludes:

"We did not prove a link between measles, mumps, and rubella vaccine and the syndrome described [autistic enterocolitis]. Virological studies are underway that may help to resolve this issue."

They also state that if there were a connection between autism and MMR then:

"a rising incidence might be anticipated after the introduction of this vaccine in the UK in 1988."

After the publication of this research the possibility of rising incidence was quickly examined. A major retrospective study was carried out in Finland, where MMR has been used for a number of years (2). More than 1.5 million children were immunised against MMR between 1982 and 1996 and the researchers claimed that no link with an increased prevalence of autism could be established.

However, the methodology of this research was heavily criticised by a number of experts, including Dr Lorna Wing. Of the records examined, it was only those of the 31 children who had shown signs of gastro-intestinal problems which had also been followed up for autism.

This study was followed by two further studies that examined the prevalence of autism since the introduction of MMR. Both stated that such a link does not exist. The first report, published in 'Current Problems in Pharmacovigilance' (3) describes an analysis of 92 cases of autism and 15 cases of Crohn's disease where the parents felt that vaccines had caused the problems. They found no evidence of extraordinary features in these cases that would suggest a new or novel type of autism. However, they did stress that:

"It was impossible to prove or refute the suggested associations between the MMR vaccine and autism or inflammatory bowel disease because of the nature, the self-selection of the cases and the lack of comparators. Nevertheless, the working party found that the information available did not support the suggested causal associations or give cause for concern about the safety of MMR or MR vaccines."

The second study (4) was specifically commissioned by the Department of Health to examine the concerns raised about MMR and autism. The researchers who conducted the study were based at the Royal Free Hospital and examined the medical records of 498 children with autistic spectrum disorders (ASDs) living within the North Thames Health Authority region. They found clear evidence that there has been a significant rise in the prevalence of autism since the introduction of MMR in 1988. However, they also found that countries that have not used the MMR vaccine also experienced this increase, and concluded:

"Our results do not support the hypothesis that MMR vaccination is causally related to autism, either its initiation or to the onset of regression - the main symptom mentioned in the paper by Wakefield and others. This study does not rule out the possibility of a rare idiosyncratic response to MMR. However, if such an association occurs, it is so rare that it could not be identified in this large regional sample."

The organisation 'Allergy Induced Autism' reacted strongly to this report, releasing a statement which strongly criticised both the methodology and the conclusions drawn from this research. It claims that:

"This study is a case series analysis, a weak form of epidemiological analysis that can only suggest or refute very large relationships. The authors begin by admitting the intrinsic flaws in the available data whilst clarifying the aim of the study as to look for evidence of a change in trend in incidence or age at diagnosis associated with the introduction of the MMR vaccine."

In 2001, the Medical Research Council (MRC) commissed an Autism Review (5). An expert group of scientists and doctors, brought together by the MRC, looked at MMR, amongst other possible factors, as a possible cause of ASDs. It concluded that the current epidemiological evidence does not support the proposed link of MMR to ASDs. Their conclusions are consistent with previous MRC reviews and with the findings of other expert groups that have reviewed this question. This report is available on the web by following this link. You can also request a hard copy of the report from the MRC (please see contact details at the end of this article). 

The 2001 review was followed by another study, funded by the MRC, at the London School of Hygiene and Tropical Medicine in 2004 (6). The research team analysed the medical records of children registered with general practices across England and Wales. They compared the vaccination histories of children who had been diagnosed with a pervasive developmental disorder (PDD) or autism with those that had not received a diagnosis. This included 1,294 children who had received a diagnosis between 1987 and 2001 and 4,469 children of the same sex and similar age who had not received a diagnosis. The team were unable to establish a link between MMR and autism or PDD.

As many ASDs are not diagnosed before the age of three, the researchers followed this with a study of children who had received the MMR before their third birthday. They were still unable to establish a link between MMR and autism.

More recently, the debate over the MMR and autism has resurfaced with two new studies receiving media attention. In 2005, a Japanese study (7), carried out jointly with Michael Rutter at the Institute of Psychiatry, London, concluded that there was no causal link between the MMR and autism. They studied over 30,000 children in the city of Yokohoma in Japan. The MMR was withdrawn from Japan in April 1993 over concerns that the anti-mumps component was causing meningitis. Since then, single vaccinations have been administered, though the government is planning to introduce another version of the MMR.

Despite this, the study found that the number of children with autism in Yokohoma continued to rise. They studied 31,426 children born in one district of Yokohama between 1988 and 1996. They found the cases of autism continued to rise after the MMR was withdrawn. 48 to 68 cases per 10,000 children were recorded before the withdrawal, to 97 to 161 per 10,000 after the withdrawal.

The same pattern of results was also seen in incidence of a particular form of autism in which children appear to develop normally and then regress, which was linked to MMR in Dr Wakefield's study. However, the study could not rule out the possibility that MMR triggers autism in a tiny number of children, which is what some have claimed.

Hideo Honda of the Yokohama Rehabilitation Centre concluded that the vaccine cannot have caused autism in the many children with autistic spectrum disorders in Japan who were born and grew up in the era when MMR was not available. Michael Rutter has also said that it rubbished the link between MMR and the general rise in autism. However, critics have said they would like more conclusive proof from UK-based studies before being convinced of MMR's safety.

The second recent study was the Cochrane Review, also in 2005 (8). Researchers searched international databases and found 139 studies assessing the effects of MMR in children. 31 studies from the original 139 were included in the review, with the others discarded due to possible bias or error. No evidence was found linking MMR with either autism or Crohn's disease.

The lead author Dr Demicheli concluded that all the major unintended events, such as triggering Crohn's disease or autism, were suspected on the basis of unreliable evidence. However, critics of the study have pointed to the fact that in the abstract of this report, the design and reporting of safety outcomes in MMR vaccine studies, both pre- and post-marketing, are largely inadequate. Some critics have also argued that the studies that were reviews lacked sufficient statistical power to detect an association between MMR causing regressive autism in a small percentage of children (9).

The debate has continued into 2006. The media has recently reported on another study in the USA that concluded there may be a link between the vaccination and the development of regressive autism. This study has been led by Arthur Krigsman at New York University. He studied 275 children with an ASD. Some of the children were found to have serious inflammation in the intestine. 82 children had gut biopsies carried out and 70 were found to show evidence of the measles virus in their gut.

Steve Walker, professor at Wake Forest University Medical Centre, North Carolina, carried out the gut biopsies. He believes that the work confirmed that done by Professor Wakefield. All the children had autism and had digestive problems. However, they did not carry out a control study with children who had not developed an ASD. This study is being presented at the International Meeting for Autism Research in Montreal. It has not been published in a journal as yet so has not been independently peer reviewed.
Other studies will continue to be done in this field. In 2004, it was announced that Professor Jean Golding would lead one of the largest studies looking at possible environmental risk factors in developing an ASD. Vaccinations are being investigated as well as difficult births, maternal and infant infection, digestive problems and maternal diet, amongst others.

Professor Golding said:

"Because of the number of children we'll be looking at, and the quality and type of data available, our study should help find the answers to a number of currently unanswered questions about the environmental risks for developing autism spectrum disorders."

No results from Professor Golding's study have yet been published.

What about the MMR booster?

An MMR booster is given to children just before they start school. The Autism Helpline has received a number of calls from parents concerned about this second vaccination, especially from families who have had a child recently diagnosed with autism. They are often concerned about giving their child or a sibling the second booster. To our knowledge, there is no research looking at the second booster and how this may affect a child with an ASD or a family member. The research so far has focused on the first dose and its possible links with a regressive form of autism.

Are there alternatives to the MMR vaccine?

The alternatives to MMR at present are either not to vaccinate or to have the vaccines administered individually at annual intervals. However, there is no research into the efficacy or timing of single monovalent vaccines against the triple MMR vaccination. For this reason parents cannot assume that following one route would be safer than the other.

Some parents have requested monovalent (single) vaccines but have met with reluctance on the part of their family doctor. The Department of Health is understandably concerned that if three injections have to be administered, then many children will miss the last two and not receive full immunity.

There is no source of single licensed measles or mumps vaccines in this country. However, monovalent vaccines may be given in this country where a child has an allergy which may make the standard vaccine unacceptable, or where the child has already begun a course of single dose vaccines, so it is worth asking your GP whether he or she is willing to administer them.

If your GP turns you down there may be a number of private practitioners prepared to administer monovalent vaccines. The vaccinations that are being offered privately are unlicensed, which means there has been no British testing on their safety and efficacy.

If parents choose not to vaccinate their children then they are currently placing them at great risk. Uptake of the MMR vaccine has dropped. In 2005, 73.3% of children under the age of five were given the vaccination. This is below the 95% level recommended by the World Health Organisation to prevent outbreaks of disease.

We realise that many parents will still be concerned; for this reason we have included the details of a number of other organisations that are also interested in this field. These groups are willing to freely discuss their views on the controversy surrounding MMR and some have details of private practices that have the single vaccination.


If you require further information please contact the NAS Autism Helpline
Tel: 0845 070 4004
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© The National Autistic Society 2003