Vaccine Safety > Issues of Interest > Autism
CDC
Research on Vaccines & Autism
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At
a glance: Several studies
have looked at whether there is
a relationship between vaccines
and autism. The weight of the evidence
indicates that vaccines are not
associated with autism. However,
CDC recognizes that some parents
and others may have concerns about
this issue. We have conducted
several studies and are continuing to explore
if vaccines are linked to autism.
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Contents of this page: |
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Related
pages and information: |
IOM = Institute of Medicine
MMR=Measles, Mumps, and Rubella
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Is CDC conducting studies to see if there
is a link between vaccines and autism?
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Yes.
CDC is committed to protecting the health
of children and to identifying the biological
and environmental causes of autism and
other developmental disabilities. This
includes further evaluating the role
of vaccines. CDC
research on vaccines and autism include:
Age
at First Measles-Mumps-Rubella
Vaccination in Children
With Autism and School Matched
Control Subjects: A Population-Based
Study in Metropolitan Atlanta.
This study conducted with the National
Center for Birth Defects and Developmental
Disabilities used data from the first
ongoing surveillance program for autism
in the United States which is helping
CDC monitor changes in the rate of
the disorder over time. The study's
results showed children with autism
received their first MMR (Measles-Mumps-Rubella)
vaccination at similar ages as children
without autism.
Also see Questions
and Answers about this study.
Reference: DeStefano
F, Bhasin
TK, Thompson
WW, Yeargin-Allsopp
M, Boyle
C. Age
at first measles-mumps-rubella vaccination in children with
autism and school-matched control subjects: a population-based
study in metropolitan atlanta. Pediatrics.
2004 Feb;113(2):259-66
Immunizations
& Possible Developmental
Regression.
CDC is working with the National Institutes
of Health to conduct a study that
will evaluate whether Measles, Mumps,
Rubella (MMR) vaccination is linked
with developmental regression, which
occurs in a subset of children with
autism.
Safety
of Thimerosal-Containing Vaccines-Vaccine
Safety Datalink Study (Pediatrics
11/03).
The CDC analyzed data to evaluate
possible associations between exposure
to thimerosal as a preservative in
vaccines and autism. Final results
showed no associations between thimerosal
and autism
or attention deficit disorder (ADD).
Reference: Verstraeten
T, Davis RL, DeStefano F, Lieu TA, Rhodes PH, Black
SB, Shinefield H, and Chen RT. Safety
of Thimerosal-Containing Vaccines: A Two-Phased Study of
Computerized Health Maintenance Organization Databases. [Journal: Article] Pediatrics.
Vol. 112(5)(pp 1039-1048), 2003.
The
Thimerosal and Autism Study.
CDC is conducting a study through the
Vaccine Safety DataLink in which
thimerosal exposure in children with
autism is being compared with children
who do not have autism. The cases of
children with autism are being evaluated
in-person by certified specialists
using the most up-to-date standardized
diagnostic assessments. Researchers
also are reviewing medical records
and interviewing children's parents
to assess any factors that could influence
the study's findings. The study is
anticipated to be completed in September
2008.
The
Autism and Biopsy Study.
This study is investigating the
question of whether the MMR vaccine may cause autism by
a mechanism involving persistent measles virus infection
in the intestine. This study involves examining the intestinal
tissue of children with autism for the presence of measles
virus. Results are anticipated in June 2007.
The
Denmark MMR/Autism study (The
New England Journal of Medicine
11/02).
This was a large-scale population based
study where researchers evaluated the
possible association between the MMR
vaccine for all children born in Denmark
between 1991 through 1998. Children
who were vaccinated with the MMR vaccine
were compared with children who were
not vaccinated with the MMR vaccine.
No increased risk of autism was found
among children vaccinated with MMR
and no association was found between
the age at the time of vaccination,
the time since vaccination, or the
date of vaccination and the development
of autism.
Reference:
Madsen KM, Hviid A, Vestergaard M,
Schendel D, Whlfahrt J, Thorsen P,
Olsen Jo, and Melbye M.
A
Population-based Study of Measles, Mumps,
and Rubella Vaccination and Autism. [Journal: Article]
Ugeskrift for Laeger. Vol. 164(49)(pp
5741-5744), 2002. Date of Publication:
02 Dec 2002.
For
more information on autism &
vaccination go to: http://www.cdc.gov/nip/vacsafe/concerns/autism/autism-mmr.htm
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First
MMR Vaccination in Children with Autism,
Atlanta Study |
Questions answered on this page:
- What
was the goal of this study?
- Why
did CDC conduct this study?
- What
were the major findings and conclusions
of CDC's study on the age of first
MMR vaccination for children with autism
compared with children who do not have
autism?
- How
did CDC researchers determine which
children had autism and at what age
they received their first MMR vaccination?
- What
were the specific groups of children
assessed to see if they were at increased
risk for autism from their first MMR
vaccination?
- What
do these findings mean for parents?
- How
many other studies have been done to
investigate the possible association
between autism and the MMR vaccination?
- What
are the known causes of autism?
- Does the MMR vaccine contain thimerosal?
- Can
vaccines that contain thimerosal cause autism?
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What was the goal of this study?
The
main goal of this study was to see if there
was a difference in the age at which children
with autism and without autism received their
first MMR vaccination. If an association existed
between the MMR vaccine and autism, children
vaccinated at younger ages (less than 24
months of age) would be expected to have a higher risk of
developing autism. Autism is usually
identified before 24 months of age.
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Why did CDC conduct this study?
Autism
is a serious life-long developmental disability.
CDC is dedicated to understanding
better the causes of autism. Because the
measles-mumps-rubella (MMR) vaccination
has been suggested as a possible cause
for autism, the CDC conducted a large-scale,
population-based study in Metropolitan
Atlanta to examine this relationship.
This study is an example of our ongoing
efforts to examine vaccine safety issues
of concern to parents, health care providers,
and others who are concerned about this
condition.
More information on CDC’s
efforts related to understanding the causes of autism is
available at
http://www.cdc.gov/programs/bd02.htm.
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What were the major findings and conclusions
of CDC's study on the age of first MMR vaccination
for children with autism compared with children
who do not have autism?
The study findings showed:
- Children
with autism received their first MMR
vaccination at similar ages as children
without autism.
- The
majority (84%) of children with and without
autism received their first MMR vaccination
before they were 24 months old
- Children
who received their first MMR vaccination
before they were 24 months old showed
no increased risk for autism regardless
of their age at the time of study, sex,
race, maternal age or maternal education.
- There
was no increased risk for autism or any
forms of autism including children whose
condition included a loss of developmental
skills (regression) associated with vaccination
before 24 months of age.
- Children
with autism were slightly more likely
to have been vaccinated before three
years of age. It is likely that these
results were influenced by factors
related to the treatment of children
with autism at this age. For example,
children with autism might have been
more likely than children without
autism to have been vaccinated as
a requirement for enrollment in preschool
special education programs that start
for children who are 3 years old.
The majority of children (98%) with
autism, between 3 to 5 years of age
in this study were enrolled in these
programs.
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How did CDC researchers determine which children
had autism and at what age they received
their first MMR vaccination?
This
study was a large-scale, population-based,
case-control study which also assessed
the possible association between autism
and the MMR vaccination for specific groups
of children who may have been
at increased risk for autism. CDC researchers,
clinical psychologists and developmental
pediatricians identified children with
autism (624) and children without autism
(1824) in Metropolitan Atlanta who were
3 to 10 years of age in 1996. They did
this by reviewing data from the Metropolitan
Atlanta Developmental Disabilities Surveillance
Program (MADDSP) and by carefully reviewing
information from special education records
and treatment providers to ensure that children
with autism were correctly identified. Vaccination
records from children's school records were
used to determine the age at which these
children had received their first dose of
MMR vaccination.
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What were the specific groups of children
assessed to see if they were at increased
risk for autism from their first MMR vaccination?
One
of the main contributions of this study is
that it assessed associations in specific
groups of children who may have been at increased
risk for autism from environmental exposures,
such as vaccines. These groups included:
- Children
who either lost developmental skills (regression)
or failed to make progress (plateau);
- Children
with developmental delays before one
year of age or with a pre- existing
condition that would likely contribute
to a developmental delay;
- Children
with or without mental retardation (which
was defined as an IQ of less than or equal
to 70); and
- Children
grouped according to characteristics such
as gender, race, and birth weight.
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What do these findings mean for parents?
These findings suggest that:
- The
MMR vaccine did not cause autism in the
general population or among specific groups
of children who may have been at an increased
risk for autism
- The
current recommended age for the MMR vaccine
(12 to 15 months) is not a contributing
factor toward autism. The study findings
showed that this was true for children
who received their MMR vaccination before
they were 24 months old; and applied to
all children in the study regardless of
their age, sex, race, or age and education
level of their mothers.
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How many other studies have been done to
investigate the possible association between
autism and the MMR vaccination?
There
have been several population-based published
studies, including this one, to investigate
the possible association between autism and
MMR vaccination. They have been conducted
in countries around the world including England,
Sweden, Denmark, and the U.S. The weight
of the evidence from these studies does not
support an association between the MMR vaccine,
or vaccines of any kind, and autism.
There
have been two laboratory studies suggesting
a possible connection between MMR vaccination
and autism. These studies have raised
the question of whether the MMR vaccine
could have caused a persistent measles
virus infection of the intestines resulting
in a unique syndrome of regression in
development and gastrointestinal disorders
in some children with autism. The study,
however, was not able to distinguish if
the intestinal infection was from a vaccine
virus or from naturally occurring measles
virus. The mechanism of how an infection
of the intestine could lead to brain damage
resulting in autism has not been established.
The population-based studies have not
found evidence of a unique syndrome of
developmental regression and gastrointestinal
disorders associated with MMR vaccine.
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- What
are the known causes of autism?
No
one knows exactly what causes autism, but
scientists think that both genetic and environmental
factors may play a role.
Family
studies have shed the most light on the genetic
contribution to autism. Studies of twins
have shown that in identical twins there
is about a 75% rate of both twins having
autism, while in non-identical twins this
occurs about 3% of the time. The risk of
autism in siblings ranges from 2 to 6 percent.
And in families with autism, there are often
other developmental problems as well, such
as language delays or learning disabilities.
The inheritance pattern is complex and suggests
that a number of genes are involved.
Autism
also tends to occur more frequently than
expected among individuals who have certain
other medical conditions, including Fragile
X syndrome, tuberous sclerosis, congenital
rubella syndrome, and untreated phenylketonuria
(PKU). Some harmful substances ingested during
pregnancy also have been associated with
an increased risk of autism, specifically,
the prescription drug thalidomide.
We
do know that parental child-rearing practices
do not cause autism.
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- Does the MMR vaccine contain thimerosal?
No
MMR vaccine has ever contained thimerosal.
Today, with the exception of some flu vaccines, none of the vaccines used in the U.S. to protect preschool children against infectious diseases contain thimerosal as a preservative. The minute amounts of thimerosal found in a few of the recommended childhood vaccines are an unavoidable by product of the production process and no harmful effects have ever been reported or found with these doses of thimerosal in vaccine.
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- Can vaccines that contain thimerosal cause autism?
Although the evidence is strong that the MMR vaccine does not cause autism, new concerns have developed about possible neurodevelopmental effects, including autism, from exposure to the mercury-containing preservative, thimerosal. Thimerosal was used in certain vaccines given to infants prior to 1999. No association has been verified between any serious health outcomes and the use of thimerosal as a preservative in vaccines.
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