MMR Vaccine and Autism

This information is courtesy of the CDC.

1. Does the MMR vaccine cause autism?

CDC believes that the current scientific evidence does not support the hypothesis that MMR, or any combination of vaccines, cause the development of autism, including regressive forms of autism. A suspected link between MMR vaccine and autism has been suggested by researchers and some parents of children with autism. Often symptoms of autism are first noted by parents as their child begins to have difficulty or delays in speaking after age one. MMR vaccine is first given to children at 12 to 15 months of age. Therefore, an apparent onset of autism within a few weeks after MMR vaccination may simply be an unrelated chance occurrence.

An extensive study of the evidence was recently conducted in the United Kingdom. The British Committee on Safety of Medicines convened a "Working Party on MMR Vaccine" to conduct a systematic review of reports of autism, gastrointestinal disease, and similar disorders after receipt of MMR or measles/rubella vaccine. The National Childhood Encephalopathy Study (NCES) was examined to see if there was any link between measles vaccine and neurological events. The researchers in England found no indication that measles vaccine contributes to the
development of long-term neurological damage, including educational and behavioral deficits (Miller et al 1997).

A more recent epidemiological study also found no association between MMR vaccine and autism (Taylor et al. 1999). This study looked at the timing of autism in relation to MMR vaccination. It found no evidence of clustering after vaccination. Also, MMR vaccination rates in autistic children were the same as in the general population.

2. What about the study by Dr. Andrew Wakefield, of the Royal Free Hospital in the United Kingdom?

Current scientific evidence does not support the hypothesis that the MMR vaccine, or any combination of vaccines, causes the development of autism, including regressive forms of autism. This includes the research conducted by Dr. Wakefield.

The Wakefield Study

This study was conducted in 1998 and looked at whether the existence of the measles virus from the MMR vaccine could cause bowel disease and, in turn, cause autism. The authors reviewed reports of 12 children with bowel disease and regressive developmental disorders, mostly autism. In 9 of the cases, the child's parents or pediatrician speculated that the MMR vaccine had contributed to the behavioral problems of the children in the study.

This study was reviewed by an expert committee from the UK Medical Research Council (MRC). The Council concluded there is no evidence to link the MMR vaccine with autism. On April 3, 2000 the MRC issued a new report confirming its earlier conclusion; MMR has not been linked with inflammatory bowel disease in autism. A copy of this research report can be found at the MRC web site, http://www.mrc.ac.uk.

Limitations of Dr. Wakefield's Study

1. The study used too few cases to make any generalizations about the causes of autism; only 12 children were included in the study. Further, the cases were selected by researchers and may not be representative of many cases of autism.
2. There were inadequate groups of control children. As a result, it is difficult to determine whether the bowel changes were similar to changes in normal children, or to determine if the rate of vaccination in autistic children was higher than in the general population.
3. The study did not identify the time period during which the cases were identified.
4. In at least 4 of the 12 cases behavioral problems appeared before the onset of symptoms of bowel disease; that is, the effect preceded the proposed cause. It is unlikely, therefore, that bowel disease or the MMR vaccine triggered the autism.

3. Would it be safer to separate the MMR vaccine into its individual components—in other words, give children three separate shots, at different times (e.g., six months or one year apart), instead of one combined shot? Why do we have to use the combined vaccine?

There is no scientific research or data to indicate that there is any benefit to separating the MMR vaccine into its individual components. This idea is not based on any published evaluation of the effect(s) it may have on children. In fact, splitting the MMR vaccine into three separate doses may be harmful because it would expose children unnecessarily to potentially
serious diseases. For instance, if rubella vaccine were delayed, 4 million children would be susceptible to rubella for an additional six to 12 months. This would potentially allow otherwise preventable cases of congenital rubella syndrome (CRS) to occur. Infection of pregnant woman with "wild" rubella virus is one of the few known causes of autism. Thus, by preventing infection of pregnant women, rubella vaccine also prevents autism.

4. Should a younger sibling, or a child of someone who suffered autism be vaccinated with MMR or other vaccines?

Current scientific evidence does not support the hypothesis that MMR, or any combination of vaccines, cause the development of autism, including regressive forms of autism.

While family history may need to be considered in specific circumstances, no contraindications to vaccination exist solely on this basis. Genetic susceptibility to severe events is worthy of further research. A younger sibling or the child of someone who suffered a vaccine adverse event usually can, and should, safely receive the same vaccine. This is especially true since the large majority of adverse events after vaccination are local reactions and fever, which do not represent a contraindication.

Due to the general safety of vaccines, and the rarity of serious vaccine adverse events, it is extremely difficult to study whether a subgroup (e.g., family members) are actually at increased risk compared with the general population. The one exception is an increased risk of neurologic events—primarily febrile seizures—after vaccination with DTP vaccine and measles-containing vaccines (MCV). The risk increases if any of these have previously occurred in immediate family members. Considering the rare occurrence of these events after DTP and MCV vaccination, the generally benign outcome of febrile convulsions, and the risk of pertussis
and measles to unvaccinated people and the general population, the Advisory Committee on Immunization Practices concluded that a history of convulsions in siblings or parents should not be a contraindication to pertussis or measles vaccination. Special care in the prevention of post-vaccination fever may be warranted in children with a family history of seizures, however. Oral polio vaccine (OPV) is contraindicated when there is a family member with immune-deficiency since OPV can spread to family contacts.

5. Should we delay vaccination until we know more about the negative effects of vaccines?

There is no convincing evidence that vaccines such as MMR and hepatitis B cause long term health effects. On the other hand, we do know that people will become ill and some will die from the diseases these vaccines prevent. Discontinuing a vaccine program based on unproven theories would not be in anyone's best interest. Isolated reports about these vaccines causing long term health problems may sound alarming at first. However, careful review of the science reveals that these reports are isolated and not confirmed by scientifically sound research.

Detailed medical reviews of health effects reported after receipt of vaccines have often proven to be unrelated to vaccine but related to other health factors. Because these vaccines are recommended widely to protect the health of the public, research into any theory about their safety is important to follow and further investigate. Several studies are currently underway to further investigate whether suggested long term effects are real or false signals.

6. I have heard that measles virus was found in specimens from intestines of children with autism? Have these data been reviewed by other scientists?

The recently released finding has not yet been published in a scientific journal. This means that it has not been reviewed by other medical experts, before and after publication, to assure the methods of the study are sound. No other laboratories have had similar findings. Such tests should be repeated by several laboratories to ensure accurate results. Several renowned measles laboratories have offered to duplicate the tests in order to validate the results. This is a typical procedure that is followed in medical research.

7. What if multiple laboratories confirmed the presence of measles virus in specimens from the intestines of children with autism? Would that indicate that measles causes autism?

Even if measles virus were consistently shown to be present in intestinal specimens of children, this would not conclusively indicate that measles causes autism. It is possible that the measles virus persists in the intestines of children with autism, i.e, the measles virus in the intestine is a side effect of autism, not a cause. In addition, in order to implicate measles virus as a cause of autism, it would be important to show that measles virus is not present in the bowel of healthy children who are of the same age as the autistic children and have the same history of measles infection and the same vaccination status. Also, there is no scientific evidence to show how intestinal inflammation with measles virus would cause the chronic neurological and behavioral difficulties seen with autism.

8. What if measles virus is shown to be associated with autism? Would that mean we should stop vaccinating against measles?

If measles virus is shown to be associated with autism, it would be most likely that the wild measles virus would be a greater cause of autism than vaccine virus. Therefore, it is likely that in preventing wild measles virus infections, we also would be reducing the total number of cases of autism. People infected with wild type measles virus develop severe infections.

Vaccination exposes the child to a weaker measles virus and prevents the complications of these severe infections. As an example, a severe degenerative infection of the brain (sub-acute sclerosing panencephalitis or SSPE) can occur following wild—type measles virus infection. Vaccine virus does not cause this severe degenerative infection and vaccination programs in the United States have virtually eliminated such complications by controlling measles.

Important disclaimer: The information on pkids.org is for educational purposes only and should not be considered to be medical advice. It is not meant to replace the advice of the physician who cares for your child. All medical advice and information should be considered to be incomplete without a physical exam, which is not possible without a visit to your doctor.