Has the rate of autism increased since the MMR vaccine has been in use?

Data from a study of California school children have been used to illustrate an increase in cases of autism since the introduction of combined measles, mumps, and rubella (MMR) vaccine.

However, the data have been presented inaccurately. A scientist reviewing the data lists several reasons why the data are misrepresented.

For example:

1. The figures presented are based on absolute numbers of children with autism, not on the rate of autism in the population. Therefore, increases in the population, even if the rate of autism is the same, will result in a higher number of autistic children.

Further, since the majority of autism is diagnosed in children, if the number of children in a population increases, even if the total number of the population stays the same, there will be a greater number of autistic children diagnosed. These studies did not account for population growth and changes in the composition of the population when announcing their results.

2. During the period of the study, there were changes in how autism was defined. If the definition of autism were made broader, then more children might meet the criteria for autism. The rate of autism would appear to increase, even if the disabled children were there all along, but had an alternate diagnosis, such as obsessive compulsive disorder or Tourette’s syndrome. This study did not control for a changed diagnostic definition of autism, so the results are not reliable.

3. An increased interest in the disease and federal funding for early intervention services occurred during this time. Therefore, parents may have been made aware of signs or symptoms of autism and had their children diagnosed earlier. The increased amount of federal funding for early intervention services gave school systems the financial means and social encouragement to have more children evaluated for autism. This may have resulted in children being diagnosed at earlier ages and an increased  number of reported cases.

A medical study performed in 2001 used the autism case numbers provided by the California Department of Developmental Services and compared them with early childhood MMR immunization-level estimates for California children. Results showed that for children born from 1980 through 1987, there was no major change in MMR immunization levels with the exception of a small increase in children born in 1988. After this small “bump” in the rate, the immunization rate returned to its previous steady level in children born through 1994. If one assumed that autism was related to immunizations, then one would expect that the rate of autism would reflect the rate of immunizations.

However, when the rate of autism in California was compared with the rate of immunization, there was a significant difference. Despite the steady rate of immunization, the number of cases of autism increased markedly, from 44 cases per 100,000 live births in 1980 to 208 cases per 100,000 live births in 1994. Even if one allows that a true increase in autism has occurred and the increase is not due to changes in diagnostic

methods, diagnostic categorization, and improved identification of individuals with autism, this analysis shows that receipt of the MMR vaccine is not a factor.

This analysis argues against a link between MMR vaccination and autism. Furthermore, there are no proven biological mechanisms that would explain such a relationship. Studies of this kind can never completely rule out rare occurrences of such a reaction.

William’s comment:

Our son received all his standard childhood vaccines. We don’t feel that had anything to do with his being autistic. We vaccinated our daughter as well, who at this time is 11 months old. We had heard about the possible link between vaccines and autism and worried about it before having our daughter vaccinated. We asked our pediatrician about it and searched the Internet for information on this topic. We ultimately were convinced that it was safe for our daughter, as it was for our son.

Term:

Measles, mumps, and rubella (MMR) – vaccine

A vaccine against measles, mumps, and rubella given to children at 18 months and again at around 4 years.  Some parents believe it to be directly responsible for autism developing in their child.