Vaccinations and autism:

Overview:  Some are concerned that vaccinations may contribute to, or cause, autism in children.  Autism is a pervasive developmental disorder characterized by impairment of social behaviors and interactions.  Autistic behaviors usually appear before 2 years of age, sometimes after apparently normal development up to that point.  In the face of such potentially debilitating disease, parents and practitioners long for an explanation of why it occurs.  Currently, the mainstream medical establishment does not know the exact cause of autism, although there does seem to be some genetic link.  In looking for explanations, vaccinations have come under scrutiny.  The vaccination for measles, mumps, and rubella (MMR) is usually given starting at 12 months old.  The peak time for diagnosing autism is around 18 months of age.  This temporal relationship has thus brought vaccinations, especially the MMR, under suspicion.  This correlation was further emphasized after the publications in 1998 by AJ Wakefield who was studying autistic children with gastrointestinal complaints.  In the author’s discussion, he implicated that the MMR vaccine could not be ruled out as a causative feature.  This conclusion was not based on the design of his study, but rather was given as one possible explanation and the author indicated that further studies would need to be done.  Although the report generated a large scare, further studies did not substantiate the link.

Temporal relationship between MMR vaccination and autistic symptoms:

Because two things happen sequentially, does not mean that they are causally related.  For example, if a rooster crows every morning and then the sun comes up, it does not mean that the rooster crow is causing the sum to come up.  In the same way, if a child receives a vaccination and then he develops autism it does not mean that the vaccination caused the autism. There must be more evidence linking them than just a temporal relationship.  If a causal relationship exists, one would expect for there to be more autism per capita in vaccinated children than in non vaccinated children.  One would also expect the rates of autism to increase after the vaccination was introduced.

Increases in the incidence of autism: 

If the MMR vaccine does cause autism, one would expect an increase in autism after widespread use of the vaccine began.  Indeed, there does seem to be an increase in the reported number of cases of autism and autism spectrum disorders after the vaccine was introduced in the US in 1971.  Explanations for this increase include changes in the diagnostic criteria of autism causing more children to be classified as autistic that were not included before, increased awareness of the disease leading to increased diagnosis, or a genuine increase in the number of autistic children.  If there was a genuine increase in the incidence of autism, the introduction of the MMR vaccine is only one of a number of variables that could be responsible for this change.  The incidence of autism in the UK did NOT increase when the MMR vaccine was introduced there in 1988. 

Results of the IOM report:

Because of concerns such as this, the link between autism and vaccinations has been carefully evaluated.  In 2000, the Immunizations Safety Review Committee convened to address the issue of a possible link between vaccinations and autism. The committee was made up of a panel which included experts in pediatrics, neurology, immunology, internal medicine, infectious disease, genetics, epidemiology, biostatistics, ethics, and other fields.   The members were carefully screened such that none of the individuals on the panel had any ties to drug manufacturing companies, had previously testified in any vaccine related cases, or been involved in any prior vaccine advisory committees.  The panel’s job was to evaluate all of the evidence then available and determine if there was enough evidence to establish a link between vaccinations and autism.  The panel came to the following conclusions:

1. The evidence favors the rejection of a causal relationship at the population level between MMR and ASD (autism spectrum disorder)
2. The evidence could not exclude the possibility that the MMR vaccine could contribute to ASD in a small number of children
3. No changes should be made to the current vaccination schedule
4. Research should be continued in this area.

Conclusion #2 was included because autism is a rare disease, occurring in approximately 15 per 10,000 people.  This makes population evaluations more difficult because there are fewer patients to study.  The panel recognized that the evidence was not sufficient to rule out the possibility of a link in a few individuals.  They admit that although they did not find a link, this does not "prove" that there is NOT a link.  However the link, if any, is only theoretical and very small. 

Weighing the risks and benefits:

The American Academy of Pediatric and the American Academy of Family Physicians continue to endorse childhood vaccination by balancing the risks of getting vaccinated against the risks of not getting vaccinated.  There is evidence that the lack of vaccination can result in illness, complications, and even death, while the risk of getting vaccinated is smaller.  On a population basis, the theoretical risk of autism is outweighed by the known risks of potentially contracting the disease. These organizations make decisions on the basis of what they perceive is good for the population as a whole.  What is best for the majority however, may be different than what is good for the individual.  Parents have a responsibility to educate themselves from reliable sources and make decisions that are truly in the best interest of their children. 

Links:

AMA:  The relationship between the MMR vaccine and autism

NIH: Why do people think that vaccines can cause autism?

Immunization Safety Review Vaccinations and Sudden Unexpected Death in Infancy