More
on Immunization and Autism
From:
Steve Eidelman
Immunization
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.
Some
parents 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.
Recent
research 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.
The
committee 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.
Moreover, 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.
Other
leading 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.
Though
the 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.
The
committee 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.
The
significance 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."
Still,
"the 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.
At
present, 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."
The
committee 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.
Further,
the 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.
"Attention
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
communication tools."
For More Information...
Information
on the Immunization Safety Review Committee can be found at
www.iom.edu/ImSafety
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.
This
study was funded by the Centers for Disease Control and Prevention
and
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.
The
Institute 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.
Permission
is granted to reproduce this document in its entirety, with
no
additions or alterations.
IMMUNIZATION SAFETY REVIEW
COMMITTEE
MARIE McCORMICK,
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.
Health Promotion
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
Staff
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
Disease Prevention
Steven M.
Eidelman
Executive Director
The Arc of the United States
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301-565-5469 - Phone
301-565-3843 - Fax
eidelman@thearc.org
http://www.thearc.org
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