By: Joy Friedman
The incidence of autism appears to be rising (1). We dont know if these higher rates are due to different diagnostic criteria, better recognition and reporting, study phenomena or if they represent a true increase in rates of autism (C. Boyle Centre for Disease Control) (2). The search for potential causes is the focus of considerable research in autism today. One hypothesis is Dr. Wakefields account of a possible link between the Measles-Mumps-Rubella (MMR) Vaccine, Inflammatory Bowel Disease (IBD) and autism (3). Although his theory is very controversial and is based originally on the observation of only 12 children with special needs (including 9 with autism spectrum disorders), the media attention it has received has left parents scared and confused. Some feel that they are forced to choose between vaccinating and possibly increasing the childs risk for autism or not vaccinating and increasing the risk of potentially life-threatening disease. This hypothesis brings two important issues to light: first, that many parents first detect symptoms of autism around 18 months of age, fairly close in time to a childs first MMR vaccination (12-15 months), and second, that the number of reported cases of autism do seem to be rising, which in some communities has coincided with the introduction of the MMR vaccine (1). The question then becomes: are these temporal relationships a coincidence or the indication of some causal factor? Over the past four years several research teams have taken on the task of trying to answer this.
The version of the MMR vaccine that is being used today was first introduced in 1979 (1). Shortly thereafter, almost the entire population was being vaccinated at an early age. Its effectiveness is remarkable, reducing the number of measles cases from 4 million in 1963 to only 100 in 1999. Measles is not a harmless disease: complication can include respiratory illness, seizures, encephalitis and even death (4). On the other hand, the MMR vaccine has had few reported side effects. A prospective study completed in 1998 by a team in Finland examined the long-term effects on children who reacted to the vaccine. Of the 3 million people vaccinated in that time period, there were 31 reported cases of children who experienced gastrointestinal problems for longer than 24 hours (often associated with fever). None of these children developed autism or had long-term effects of any kind (5). This is significant because it is in the subgroup of children with autism and gastrointestinal symptoms than the association with MMR is proposed.
Follow Up Research
The findings of studies performed by several sources, examining over 3500 individuals with PDDs following Dr. Wakefields original report challenge the connection (6). Time trend analysis has been done both in North America (1) and in Britain (7, 8) and has found that there is no relation between age of onset and age of vaccination. Furthermore, although the number of people being vaccinated has remained at over 95% from 1988 to 1999 the incidence of autism has increased seven fold demonstrating that increased incidence of autism is not related to use of the vaccine at the population level. In fact, the increased reporting of autism began to occur prior to the introduction of the MMR vaccine (1). It should be noted that this apparent increase may be due to some external factor such as broadening diagnostic criteria to include atypical and milder forms of PDDs (9). (See Dr. Szatmaris article on page 4 for information on the changes in diagnostic criteria.)
Response from Professional Bodies
Over the past year many government public health organizations have independently reviewed the present scientific literature in order to determine if changes should be made to their national health policies. The results of these analyses are published and available on the Internet (see addresses below). The most thorough of these was completed by the American Institute of Medicine (AIM) who selected a committee of professionals unaffected by the outcome of their findings. The review lead them to conclude that the evidence favors rejection of a causal relationship at the population level between MMR vaccine and autistic spectrum disorders (ASD). The committee recommended that there be no changes to health policies regarding the MMR vaccine but that research into the issue continue (6). Both the Canadian and British reviews lead to similar conclusions (10, 11).
Recommendations for Parents
The decision as to whether or not to vaccinate must be weighed by each parent. However, it is important to know that Wakefields suggestion that MMR may increase risk of autism is an unproven theory, and that extensive research worldwide has failed to substantiate this proposed link. We highly recommend that parents concerned about the safety of the vaccine read through the Executive Summary of the AIM Immunization Safety Review, to make their own conclusions about available evidence. The search for the cause(s) of autism is a long one, filled with many small steps.
1. Dales, L., Hammer S.J., Smith, N.J., Time trends in autism and in MMR immunization coverage in California. JAMA. 285(9):1183-5, 2001.
2. Vastag, B. Medical News & Perspectives: Congressional Autism Heaarings Continue: No evidence MMR vaccine causes disorder. JAMA. 285(20):2567-2569, 2001.
3. Wakefield, A.J., Murch, S.H., Anthony, A., Linnell, J., Casson, D.M., Malik, M., Berelowitz, M., Dhillon, A.P, Thomson, M.A., Harvey, P., Valentine, A., Davies, S.E., Walker-Smith, J.A. Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children. Lancet. 28;351(9103):637-41, 1998.
4. Marwick, C. US report finds no link between MMR and utism. BMJ. 322(7294):1083A, 2001.
5. Peltola, H., Patja, A., Leinikki, P., Valle, M., Cavidkin, I., Paunio, M., No evidence for measles, mumps, and rubella vaccine-associated inflammatory bowel disease or autism in a 14-year prospective study. Lancet. 351(9112):1327-8, 1998.
6. Kathleen Stratton, Alicia Gable, Padma Shetty, and Marie McCormick. Immunization Safety Review: Measles-Mumps-Rubella Vaccine and Autism, Washington DC: National Academy Press, 2001. Online: http://www.nap.edu/catalog/10101.html
7. DeStefano, F., Chen R.T. Autism and measles, mumps, rubella vaccine: No epidemiological evidence for association. Jrounal of Pediatrics, 136(1):125-6, 2000.
8. Kaye, J.A., del Mar Melero-Montes, M., Jick, H. Mumps, measels and rubella vaccine and incidence of autism recorded by general practitioners: a time trend analysis. BMJ, 322(7284):460-3, 2001.
9. Halsey, N.A., Hyman, S.L. MeaslesMumps Rubella vaccine and Autistic Spectrum Disorders Pediatrics vol 107(5)pe84. Online: http://www.pediatrics.org/cgi/content/full/107/5/e84
10. Stauss, B., Bigham M. Does measles-mumps-rubella (MMR) vaccination cause inflammatory bowel disease and autism? Canada Communicable Disease Report. 27(8):65-72, 2001. Online: www.hc-sc.gc.ca/hpb/lcdc/publicat/ccdr/01vol27/dr2708e.html.
11. Measles, Mumps and Rubella Vaccine, United Kingdom: Department of Health, 2001. Online: http://www.doh.gov.uk/mmr.htm