Written By - Dr. Kim Riviello, DNP, MBA, CRNA
Autism is a developmental disability that comes from a neurological disorder affecting the brain. It is characterized by abnormal communication, social, and reasoning skills. The symptoms are usually not present until approximately 30 months of age at which time the child will start to exhibit fixation on inanimate objects, inability to communicate normally, and resistance to change in daily activities. They are unable to hold eye contact, display unmotivated temper tantrums, insensitivity to pain, and repetition of words and phrases. The degree of these symptoms can vary widely. One-quarter of these children develop seizures and two-thirds are diagnosed as mentally retarded ("Autism," 2011).
Autism has no known single cause. There are no two children with autism alike, which makes scientists believe that it is a variety of factors that cause autism. The genetic disposition of the child has been determined a primary factor. Specifically what occurs with the genes is unknown but it appears to be related to gene mutation or genetic variants. Environmental factors such as viral infections and pollutants have also been suggested as triggering agents for autism ("Autism-Mayo," 2012).
From mid-1980 to mid-1990 the incidence of autism increased from 1 in approximately 2500 to 1 in approximately 300 children, respectively. This increase coincided with the increase in the number of childhood vaccines being administered (Novella, 2008). This supposed association was investigated by Wakefield in 1998 when twelve children presented with pervasive developmental disorder, gastrointestinal symptoms and developmental regression. Eight of the twelve children had behavioral changes associated with the MMR vaccine according to retrospective accounts by the parents and physicians. This study by Wakefield did not have substantial evidence to prove his hypothesis linking the MMR vaccine to autism.
The validity of the study was questionable due to the insufficient number of children and a lack of a control group. Potential bias was instilled with the data collection being dependent on retrospective memory of the parents and physicians concerning the actual symptoms of the children. The report itself refuted any connection between the MMR vaccine and the behavioral changes that the children exhibited (Wakefield et al., 1998). The one thing that Wakefield did accomplish was to introduce a possible cause for autism that left people wondering.
The increase in number of autistic cases still continues to rise. 1 in 150 children are now estimated to be diagnosed with autism (Novella, 2008). The question still remains, what is the cause and is it still possibly related to vaccines?
Since Wakefield’s study in 1998 there have been several other studies addressing the relationship of vaccines to autism. In 2001 Dewild and his colleagues conducted a case-control study of children in the United Kingdom to examine a sequential association between the MMR vaccine and autism. Dewild hypothesized that the onset of developmental regression following the MMR vaccine would be revealed in an increase in consultations with the children’s physicians. A general practice databank was employed to examine whether children who were later diagnosed with autism had more frequent consults following the MMR vaccine than children who were not vaccinated. Dewild’s study matched seventy-one children with autism and 284 matched controls during 1989 to 2000. They matched for age, sex month of MMR vaccination, and physician. The study showed no significant difference in consultations between the children with autism and the control group. During the time period, only one case of autism was diagnosed within six months of the MMR vaccination. This study being a matched-control with over 300 children being examined makes the validity of the study far more conclusive than
the Wakefield study. The only limitation found within Dewild’s research is that it included all consults not just consults specific to autism (Dewild, Carey, Richards, Hilton, & Cook, 2001).
An even stronger study rebutting the association of MMR vaccines and autism was conducted in Denmark in 2002. Madsen and his colleagues piloted a population-based retrospective study comparing the rates of autism among children who were vaccinated with MMR and those who were not. The Danish Civil Registration system was used to collect data on children born between 1991 and 1998. A total of 537, 303 children were in the cohort and followed for 2,129,864 person-years. The Danish vaccine program vaccinated children with MMR at fifteen months and twelve years of age. The data only included those children at age 15 months due to the relevance to the study. The diagnosis of autism was retrieved from the Danish Psychiatric Central Register based on ICD codes and included all children with autism. A total of 440,655 children (82 percent) received the MMR vaccine for a total of 1,647,504 person-years of follow up, compared with 482,360 person-years of follow up of children who did not receive the vaccine. A total of 316 children were diagnosed with an autistic disorder and 422 diagnosed with some other type of development disorder. The relative risk of autistic disorder among vaccinated children compared to unvaccinated children was 0.92% with a relative risk for another developmental disorder was 0.83%. Madsen and his colleagues showed that the risk of autism was comparable both in vaccinated and unvaccinated children with no sequential clustering of autism cases following immunizations, thus they concluded that the MMR vaccine was not associated with autism (Madsen et al., 2002).
Numerous other studies have been conducted repudiating the link between MMR vaccines and autism however the preservative Thimerosal, mercury based preservative contained in vaccines, has been questioned as a contributory factor. In 2004 the Institute of Medicine
(IOM) released a statement that there was no association between Thimerosal and autism based on studies they reviewed. The IOM did state that children with autism do have difficulty with excreting mercury from their systems but Thimerosal was not an influential element in the root cause of autism ("IOM Safety Review," 2004).
Due to the continued upsurge in autistic cases the CDC decided to conduct their own study on Thimerosal. They expanded their study to include impact of maternal exposure to Thimerosal while pregnant, evaluation of exposure in association with the three autism spectrum disorder subtypes, and a more rigorous approach to evaluating autism diagnosis and Thimerosal exposure. A total of 1,008 children were studied with 256 having autism and 752 did not. The study found that children with autism and those without had similar exposures to Thimerosal from pregnancy to twenty months of age. There was also no association to autism with maternal exposure to Thimerosal during pregnancy (prenatally) or as a young child. The CDC found the same results to be in male and females and the final conclusion being that Thimerosal-containing immunizations did not increase the risk of any of the autistic outcomes (Price et al., 2010).
Based on the above studies, and the numerous others not mentioned, the evidence is strong to support that there is no link concerning childhood vaccines and autism. This information needs to be conveyed to parents in order to continue the necessary vaccinations against childhood diseases.
References
Autism. (2012). Mayo-Clinic. Retrieved from http://www.mayoclinic.com/health/autism/DS00348/DSECTION=causes
Dewild, S., Carey, I. M., Richards, N., Hilton, S. R., & Cook, D. G. (2001). Do children who become autistic consult more often after MMR vaccination? []. British Journal of General Practicioners, 51(464), 226-7.
Immunization safety review: autism and vaccines. (2004). Institute of Medicine . Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK25349/
Madsen, K. M., Lauritsen, M. B., Vestergaard, M., Schendel, D., Wohlfahrt, J., Thorsen, P.,...Melbye, M. (2002). A population-based study of measles, mumps, and rubella vaccination and autism. New England Journal of Medicine, 347(19), 1477-82.
Novella, S. (2008, April 16). The increase in autism diagnosis: two hypotheses []. Science-Based Medicine. Retrieved from http://www.sciencebasedmedicine.org/index.php/the-increase-in-autism-diagnoses-two-hypotheses/
Price, C. S., Thompson, W. W., Goodson, B., Weintraub, E. S., Croen, L. A., Hinrichsen, V. L.,...DeStefano, F. (2010, September 13). Prenatal and infant exposure to Thimerosal from vaccines and immunoglobulins and risk of autism. Pediatrics, 126(4), 656-654. doi:10.1542/peds.2012-0309
Wakefield, A. J., Murch, S. H., Anthony, A., Linnell, J., Casson, D. M., Malik, M.,...Walker-Smith, J. A. (1998). Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children. Lancet, 351, 637-41.
What is autism? (2011). Autism. Retrieved from http://www.autism-pdd.net/what-is-autism.html