- Knowledgebase: Immunization Questions
- Questions about immunizations, side effects, and not vaccinating.
- 19. AAP: Q &A regarding MMR and Autism - Top
- Q. What is autism?
A. Autism is a spectrum of chronic developmental disorders. The main characteristics of autism are difficulties in social interaction, communication, and restrictive and repetitive interests and activities. Autism may be noted initially in infancy as impaired attachment, but autism is most often first identified in toddlers, mostly boys, from 18 to 30 months of age. Although there is no cure, autism is treatable. Symptoms associated with autism often improve, as children start to acquire language and learn how to communicate their needs.
Q. What causes autism?
A. The causes of autism are not known for certain. Most experts agree that autism is a condition that begins before birth. The current theory favored by many experts is that autism is a genetically-based disorder. Studies of persons with autism have identified abnormalities in brain structures that develop in the first few weeks of gestation (that is, while the fetus is in the womb). Evidence that genetics is an important, but not exclusive, cause of autism includes a 3 to 8 percent risk of recurrence in families with one affected child. Also, when one identical twin has autism, the chances are extremely high that the other twin will also have autism. A working group convened by the National Institutes of Health in 1995 reached a consensus that autism is a genetic condition. An issue unresolved by the group was the role of immune factors in certain forms of autism; it was suggested that studies to clarify the situation are needed.
Q. Why are we seeing a rise in the incidence of autism?
A. Doctors use a book called the Diagnostic and Statisical Manual of Mental Disorders to help them diagnose cases of autism. In the past decade, the guidelines in that book have changed to become more inclusive. Children who used to be considered "learning delayed" or to have "behavior problems" may now be diagnosed with mild autism. Also, parents and medical professionals appear to be more aware of the condition and more likely to pursue a diagnosis and treatment than in years past.
Q. Is there any evidence linking measles vaccine or MMR and autism?
A. The currently available evidence does not support a link between MMR and autism. Autism usually is diagnosed in children when they are 18 to 30 months old. This is a period in life shortly after children have received many of the recommended vaccinations. Because of this coincidence, some parents of children with autism believe that an immunization may have caused their child's condition. A 1998 study in the medical journal Lancet, reported that there may be a link between the measles virus and autism. Subsequent studies in the United Kingdom and in Sweden have been conducted to evaluate whether measles virus or MMR vaccine causes, or in any way contributes to, autism. Both of these studies showed no association between the MMR vaccine and autism. In a thorough review of all the evidence, the Medical Research Council in the United Kingdom found no scientific evidence supporting a relationship between MMR vaccine and autism.
Q. I have heard that measles virus was found in specimens from intestines of children with autism? Have these data been reviewed by other scientists?
A. 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.
Q. 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?
A. 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, ie, 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.
Q. What if measles virus is shown to be associated with autism? Would that mean we should stop vaccinating against measles?
A. 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.
Q. What can happen if I don't get my child immunized?
A. Without immunizations, your child can catch diseases that may cause high fever, coughing, choking, breathing problems, and even brain injury. These illnesses may leave your child deaf or blind, cause paralysis, and even death. Around 1960, there were over a half a million measles cases and more than 400 deaths associated with this disease. Thanks to immunization efforts, there were only 100 cases of measles in 1998 and zero deaths related to measles. Despite this and other successes, some parents still refuse to have their children immunized. This not only puts their child at risk, it also opens up the possibility of outbreaks in schools, child care centers and other public settings.
Q. Why should we still vaccinate against measles when cases are so uncommon?
A. Before measles immunizations were available, nearly everyone in the U.S. got measles disease. There were approximately 3 to 4 million measles cases each year. An average of 450 measles-associated deaths were reported each year between 1953 and 1963. Currently measles virus is common throughout the world and is frequently imported into the U.S. In 1998, 100 cases of measles occurred in the U.S. From 1997 to 1999 over half of the states in the U.S. were threatened with measles following importation of a case of measles from another country. A reduction in measles immunization rates would substantially increase the potential size and morbidity of any outbreak. That means we would see more people die from measles.
Q. What are the known complications of measles vaccination?
A. Measles vaccine is very safe; most people have no reactions. About 5 percent to 15 percent of vaccinees may develop a fever 5 to 12 days after MMR vaccination. The fever usually lasts one to two days and usually is not associated with other symptoms. About 5 percent of MMR recipients may develop a transient rash one to two weeks after immunization. Central nervous system disturbances, such as encephalitis, have been reported with a frequency of less than one per 1 million doses administered, a frequency many times lower than the incidence of serious central nervous system disorders that follow natural infection.
Q. Aren't measles, mumps and rubella relatively harmless illnesses?
A. Measles is a highly contagious serious viral infection. The illness is characterized by a rash, but the virus can also spread through the body causing pneumonia, diarrhea, or ear infections in up to 10% of people. In addition, it can cause an infection of the brain (encephalitis), which can cause permanent brain damage. Approximately 20% of people with measles will be hospitalized and for every 1,000 people who get measles, 1 to 2 will die. Measles vaccine (contained in MMR, MR and measles vaccines) can prevent this disease. Mumps causes fever, headache and swelling of one or both cheeks or sides of the jaw. Four to six persons out of 100 who get mumps will get meningitis, an inflammation of the lining of the brain. Inflammation of the testicles, which may lead to sterility, occurs in about 4 of every 10 adult males who get mumps. Mumps also may result in hearing loss, which is usually permanent.
Rubella is also known as German measles. Rubella is a mild disease in children and young adults, causing rash and fever for 2 to 3 days. However, rubella can cause devastating birth defects if acquired by a pregnant woman; there is at least 20% chance of damage to the fetus if a woman is infected early in pregnancy.
Q. What is being done to find the causes of autism and to ensure the safety of the MMR vaccine?
A. The U.S. Centers for Disease Control and Prevention is conducting other scientific studies to further examine any possible association between autism and the MMR vaccine. Additionally, England's Medical Research Council will fund one of the largest studies of autism ever attempted. The study will attempt to discover the causes of autism.
The CDC continues to recommend two doses of MMR vaccine for all children. The first dose is recommended at 12-15 months of age and the second dose is recommended at 4-6 years of age. Immunizations are one of the most important ways that parents can protect their children against serious infectious diseases.
For more information about immunizations, log on to www.cdc.gov/nip.
- Updated: March 5, 2001
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