Vaccines and Autism
1. What is autism?
Autism is a chronic developmental disorder. The main characteristics of autism are problems in social interaction, communication, and restrictive and repetitive interests and activities.
Autism may be initially noted in infancy as impaired attachment, but it is most often first identified in toddlers, mostly boys, from 18 to 30 months of age. Boys are 3 to 4 times more likely to be afflicted with autism than girls. Girls as a group, however, may be more severely affected. Correct diagnosis of autism depends on an accurate developmental history focused on types of behaviors typical of autism and on evaluation of current functional skills. Approximately 75 percent of persons with autism are mentally retarded. Less than 5 percent of children with autistic traits have fragile X or some other, known chromosomal abnormality.
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.
2. What are the known causes of autism?
The causes of autism are unknown in most cases. In a few cases, biologic causes have been identified, although none are unique to autism. Some prenatal factors include intrauterine rubella; tuberous sclerosis; chromosomal abnormalities, such as Down's syndrome; as well as brain abnormalities, such as hydrocephalus. Frequently cited postnatal conditions associated with autism are untreated phenylketonuria, infantile spasms, and herpes simplex encephalitis. In the majority of cases, however, no underlying cause can be identified.
The current theory favored by many experts is that autism is a genetically-based disorder that occurs before birth (Piven 1997). Studies of persons with autism are finding abnormalities in brain structures that develop in the first few weeks of gestation (that is, while the fetus is in the womb) (Rodier 1998). Evidence that genetics is an important, but not exclusive, cause of autism includes a three to 8 percent risk of recurrence in families with one affected child. 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 autism spectrum disorders; it was suggested that studies to clarify the situation are needed.
3. Is there any scientific evidence that provides a link between autism and vaccines?
To date there is no convincing evidence that any vaccine can cause autism or any kind of behavioral disorder. A suspected link between measles, mumps, rubella (MMR) vaccine and autism has been suggested by some parents of children with autism. Typically, symptoms of autism are first noted by parents as their child begins to have difficulty with delays in speaking after age one. MMR vaccine is first given to children at 12 to 15 months of age. Therefore autism cases with an apparent onset within a few weeks after MMR vaccination may simply be an expected but unrelated chance occurrence.
The only evidence that has been presented to suggest that MMR vaccine may be associated with autism has been published by the Lancet (Wakefield et al 1998 ). An editorial published in the same issue, however, discussed concerns about the validity of the study (Chen and DeStefano 1998). Based on data from 12 patients, Wakefield and colleagues speculated that MMR vaccine may have been the possible cause of bowel problems which led to a decreased absorption of essential vitamins and nutrients which resulted in developmental disorders like autism. No scientific analyses were reported, however, to substantiate the theory. Whether this series of 12 cases represent an unusual or unique clinical syndrome is difficult to judge without knowing the size of the patient population and time period over which the cases were identified. If there happened to be selective referral of patients with autism to the researchers' practice, the reported case series may simply reflect such referral bias. Moreover, the theory that autism may be caused by poor-absorption of nutrients due to bowel inflammation is not supported by the clinical data. In at least 4 of the 12 reported cases, behavioral problems appeared before the onset of symptoms of inflammatory bowel disease (that is, the effect preceded the cause). Furthermore, since publication of their original report in February of 1998, Wakefield and colleagues have published another study in which highly specific laboratory assays in patients with inflammatory bowel disease, the posited mechanism for autism after MMR vaccination, were negative for measles virus (Chadwick 1998, Duclos 1998).
Other recent investigations also do not support a causal association between MMR (or other measles-containing vaccines) and autism or inflammatory bowel disease. In one investigation, a Working Party on MMR Vaccine of the United Kingdom's Committee on Safety of Medicines (1999) was charged with the evaluation of several hundred reports, collected by a firm of lawyers, of autism, Crohn's disease, or similar disorders developing after receipt of MMR or MR vaccines. The Working Party conducted a systematic, standardized review of parental and physician information. Although acknowledging that it is impossible to prove or refute the suggested associations (because of variable data quality, biased selection of cases, and lack of a control group), the Working Party concluded that the information available "... did not support the suggested causal associations or give cause for concern about the safety of MMR or MR vaccines."
A study by Taylor and colleagues provides population-based evidence that overcomes many of the limitations faced by the Working Party and by Wakefield and colleagues (Taylor 1999; DeStefano and Chen 1999). The authors identified all 498 known cases of autism spectrum disorders (ASD) in certain districts of London born in 1979 or later and linked them to an independent regional vaccination registry. ASD includes classical autism, atypical autism, and Asperger's syndrome, but the results were similar when cases of classical autism were analyzed separately. The authors first showed that the known number of ASD cases has been increasing since 1979 and there was no jump after the introduction of MMR vaccine in 1988. Second, they found that cases vaccinated before 18 months of age had similar ages at diagnosis as did cases who had been vaccinated after 18 months or not vaccinated, indicating that vaccination does not result in earlier expression of autistic characteristics. Third, they showed that at age two years the MMR vaccination coverage among the ASD cases was nearly identical to coverage in children in the same birth cohorts in the whole region, providing evidence of an overall lack of association with vaccination. Finally, Taylor and colleagues showed that the first diagnosis of autism or initial signs of behavioral regression were not more likely to occur within time periods following vaccination than during other time periods. A weak statistical association was found between MMR vaccination and initial parental concern, but this appears to have been due to parents' difficulty in recalling precise age at onset and a preference for approximating the age as 18 months.
A study of the population of children in two communities in Sweden also found no evidence of an association between MMR vaccination and autism (Gillberg and Heijbel 1998). That study found no difference in the prevalence of autism in children born after the introduction of MMR vaccination in Sweden compared with children born before.
4. Is there a theoretical possibility that there is a connection between autism and MMR vaccine or any other vaccine?
If measles vaccine, or any other vaccine, causes autism then it would have to be a very rare occurrence since millions have children have received vaccines without ill health effects.
In January 1990, an Institute of Medicine committee examining possible health effects associated with DPT vaccine concluded that there was no evidence to indicate a causal relation between DPT vaccine or the pertussis component of DPT vaccine and autism. Also, data obtained from CDC's Monitoring System for Adverse Events Following Immunization (MASAEFI) system, showed no reports of autism occurring within 28 days of DPT immunization from 1978-1990, a period in which approximately 80.1 million doses of DPT vaccine were administered in the United States.
From January 1990 through February 1998, only 15 cases of autism behavior disorder after immunization were reported to the Vaccine Adverse Events Reporting System (VAERS). Because of the small number of reports over an 8 year period, the cases reported are likely to represent unrelated chance occurrences that happened around the time of vaccination. The most frequent vaccines cited in the reports were diphtheria, tetanus, pertussis (DPT), oral polio vaccine (OPV), and MMR. Other vaccines reported as having a possible association with autism were Haemophilus influenzae type B and Hepatitis B.
Recently, the National Childhood Encephalopathy Study (NCES) was examined to see if there was any link between measles vaccine and neurological events. 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).
With whooping cough on the rise again, and Kelly's concerns..I am wondering how many parents choose not to vaccinate their kids? I'm proud to say that my baby has had all hers and I have kept her current and will continue to do so. What about you? What are your thoughts on vaccines?