Measles-Mumps-Rubella Vaccine and Autism
on Immunization and Autism
From: Steve Eidelman
is widely regarded as one of the world's most effective tools
for protecting public health. In the United States alone,
child-vaccination programs have resulted in the elimination of smallpox and polio and
rendered once-common, often debilitating, and potentially life-threatening
infectious diseases--such as diphtheria, pertussis, and measles--exceedingly uncommon.
But along with
these benefits have come concerns about safety, making some
immunization policies a subject of public debate. One such issue is
whether or not the measles-mumps-rubella (MMR) vaccine causes autistic spectrum
disorders (ASD), frequently referred to simply as autism.
The MMR vaccine,
which comprises three vaccines given in a single shot,
has been extremely successful in virtually eliminating measles, mumps, and
rubella in the United States. Measles cases, for example, dropped from
over 400,000 per year in the pre-vaccine era to only 100 in 1999. However,
these diseases remain a serious threat in other parts of the world where
children are not routinely vaccinated. Measles alone resulted in over a million
deaths in children around the world last year.
and researchers are concerned though that the MMR vaccine
might cause ASD. Autistic spectrum disorders are incurable, permanent diseases
that result in serious developmental problems in children. Although
scientists generally agree that most cases of ASD result from events that
occur in the prenatal period or shortly after birth, there is considerable
concern because autistic symptoms typically do not emerge until the
child's second year--about the same time the MMR vaccine is first administered. In
addition, there are concerns that the introduction of wide-scale use of
MMR coincides with an apparent increase in the incidence of autism.
in Britain provides suggestive evidence of such a link. In
a highly publicized study, published in The Lancet in 1998, researchers
describe 12 children who developed behavioral problems, including ASD,
shortly after receiving the MMR vaccine. While the authors note that their
study did not prove an association between MMR and ASD, it suggests the
need for further research on this hypothesis. Since then, this group and other
scientists have further examined this potential relationship.
The CDC and
the National Institutes of Health recognized the need for an
independent group to carefully examine the hypothesized MMR-autism link
and address other vaccine-safety issues as well, in order to give some
guidance to themselves, health care providers, researchers, and a concerned public.
These agencies engaged the Institute of Medicine (IOM), which in turn
appointed the Immunization Safety Review Committee, a 15-member body of
health professionals with wide-ranging expertise in areas relevant to the
problem. To preclude any real or perceived conflicts of interest,
candidate members were subject to strict selection criteria that excluded anyone who
had participated in research on vaccine safety, received funding from
vaccine manufacturers or their parent companies, or served on vaccine
advisory committees. The results of the committee's assessment of the
issue are described in the report titled Immunization Safety Review:
Measles-Mumps-Rubella Vaccine and Autism.
has reviewed the numerous research efforts on the MMR-autism
hypothesis. "The evidence favors rejection of a causal relationship at the
population level between MMR vaccine and autistic spectrum disorders," the
committee concludes in its report. "A consistent body of epidemiological
evidence shows no association at a population level between MMR and ASD," the report says.
the committee can find no proven biological mechanisms that
would explain such a relationship. Scientists have suggested some theories, but
none have been demonstrated. For example, though it is possible that a
viral infection caused by the vaccine could invade the central nervous system,
provoke an autoimmune response and ultimately produce autism, researchers
have observed no evidence of this kind of injury. Finally, scientists have not
been able to make inferences by studying the hypothesis in laboratory
animals because of the difficulty of mimicking these conditions in animals.
medical groups--the American Academy of Pediatrics, the
World Health Organization, and British health authorities--have come to similar
conclusions for largely the same reasons.
MMR-autism question might appear to be resolved, science is
always a work in progress; a conclusion is only as good as the methods of
the analysis. The epidemiological studies, traditional public health tools
used to examine the risk factors for a disease on a population level, were
at a disadvantage here because there is little variation in exposure to
MMR since children in most developed countries are vaccinated similarly.
Furthermore, the difficulties in diagnosing and determining the exact
onset of autism in children make it difficult to design appropriate studies and
compare the results from those studies.
acknowledges they could not rule out another
possibility--that MMR vaccine could contribute to ASD in a small number of children--because
existing epidemiological tools may not have enough precision to detect the
occurrence of rare effects like ASD.
of this set of issues transcends the science alone.
Infectious diseases like measles, mumps, and rubella, left unchecked,
could cause considerable sickness and death. Public-health officials fear a
repetition of the pertussis-vaccine history of the 1970s, when the
combination of low numbers of pertussis cases and public concerns about
the vaccine's safety caused immunization rates around the world to plummet,
with sobering results. In Japan, for instance, pertussis vaccine coverage
dropped from 80% to 10% in the mid-1970's resulting in epidemic involving 13,000
reported cases and 41 deaths. "Similar disease outbreaks could easily
occur, with devastating effects," says the committee, "were immunization rates to
decline as a result of fears regarding MMR vaccine."
responsibility of the government to ensure the safety of [the
MMR] vaccine is high, even if the adverse outcome is rare," the committee
notes. The seriousness of autism - an incurable and serious behavioral
disorder - requires rigorous consideration of all possible etiologies. And
in any case, it adds, the level of public concern about MMR vaccine safety
is high and must be meaningfully addressed.
This is especially
important in that MMR vaccination is required by law in
all 50 states for entry into school and day care, in part, to protect the
health of others. These factors, the committee concludes, suggest the need
for continued attention to this issue.
however, no change of MMR immunization procedures is warranted.
The report plainly states that "The committee does not recommend a policy
review at this time of the licensure of MMR vaccine or of the current
schedule and recommendations for administration of MMR vaccine."
does propose targeted research efforts and more rigorous
data-gathering procedures. These would give scientists a firmer
understanding of MMR vaccination and any possible side effects. In
particular, the committee recommends the use of common definitions for
autism cases; more detail and documentation in their reporting; comparing
the effects of different immunization exposures; and clinical and
epidemiological studies to identify risk factors and biological markers of ASD.
committee notes that government agencies responsible for
immunization should recognize that most members of the public currently
get their information on this and other health issues from the news media and
the Internet. As a result, agencies such as the CDC and Food and Drug
Administration must actively work at providing helpful public
communications, beginning with the improved accessibility of their own Web sites.
should be given to how the material is perceived and used by
those with the right and desire to know--the parents of children about to
be immunized or those who believe their child has been adversely affected,"
the committee says. "Direct input from parents and other stakeholders would be
invaluable in conducting a systematic and effective evaluation of current
on the Immunization Safety Review Committee can be found at
Copies of Immunization
Safety Review: Measles-Mumps-Rubella Vaccine and
Autism are available for sale from the National Academy Press; call (800)
624-6242 or (202) 334-3313 (in the Washington metropolitan area), or visit
the NAP home page.
was funded by the Centers for Disease Control and Prevention
the National Institute of Allergy and Infectious Diseases of the National
Institutes of Health as part of an National Institute of Health Task Order No. 74.
of Medicine is a private, nonprofit organization that
provides health policy advice under a congressional charter granted to the National
Academy of Sciences. For more information about the Institute of Medicine,
visit the IOM home page at ww.iom.edu.
© 2001 by the National Academy of Sciences. All rights reserved.
is granted to reproduce this document in its entirety, with no
additions or alterations.
M.D., Sc.D., (Chair), Professor and Chair, Department of
Maternal and Child Health, Harvard School of Public Health
RONALD BAYER, Ph.D., Professor, Division of Sociomedical Sciences, School
of Public Health, Columbia University
ROSEMARY CASEY, M.D., Associate Professor of Pediatrics, Jefferson Medical
College and Director, Lankenau Faculty Pediatrics, Wynnewood, Pennsylvania
JOSHUA COHEN, Ph.D., Senior Research Associate, Harvard Center for Risk
Analysis, Harvard School of Public Health
VERNICE DAVIS-ANTHONY, M.P.H., Senior Vice President, Corporate Affairs
and Community Health, St. John Health System, Detroit, MI
BETSY FOXMAN, Ph.D., Professor, Department of Epidemiology, School of
Public Health, University of Michigan
CONSTANTINE GATSONIS, Ph.D., Professor of Medical Science and Applied Math,
and Director, Center for Statistical Sciences, Brown University
STEVEN GOODMAN, M.D., M.H.S., Ph.D., Associate Professor, Department of
Oncology, Division of Biostatistics, Johns Hopkins School of Medicine
ELLEN HORAK, M.S.N., Chief of Local Services, Office of Local and Rural
Health, Kansas Department of Health and Environment
MICHAEL KABACK, M.D., Professor, Pediatrics and Reproductive Medicine,
University of California, San Diego
Gerald Medoff, M.D., Professor, Department of Internal Medicine,
Washington University School of Medicine
REBECCA PARKIN, Ph.D., Associate Research Professor, Department of
Occupational & Environmental Health, School of Public Health and Health
Services, George Washington University
BENNETT SHAYWITZ, M.D., Professor of Pediatrics and Neurology,
Co-Director, Yale Center for the Study of Learning and Attention
CHRISTOPHER WILSON, M.D., Professor and Chair, Department of Immunology,
University of Washington
ALFRED BERG, M.D., M.P.H., Professor and Chair, Department of Family
Medicine, University of Washington School of Medicine is a member of the
Immunization Safety Review Committee, but was unable to attend the meeting
on the topic of this report.
and Disease Prevention Board Liaison
RICHARD B. JOHNSTON, Jr., M.D., Professor of Pediatrics, Department of
Pediatrics, University of Colorado School of Medicine and National Jewish
Medical & Research Center
KATHLEEN STRATTON, Ph.D., Study Director
ALICIA GABLE, M.P.H., Program Officer
PADMA SHETTY, M.D., Program Officer
DONNA ALMARIO, Research Associate
KYSA CHRISTIE, Research Assistant
ANN ST. CLAIRE, Senior Project Assistant
ROSE MARIE MARTINEZ, Sc.D., Director, Board on Health Promotion and
Steven M. Eidelman
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