By: Joy Friedman
Background
The
incidence of autism appears to be rising (1). “We
don’t 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. Wakefield’s
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 child’s 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 child’s 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. Wakefield’s 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. Szatmari’s
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 Wakefield’s 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.
References
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. Measles—Mumps– 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