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Vaccine
Safety > Issues of Interest > Thimerosal
Thimerosal
& Vaccines
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Why
is thimerosal used as a preservative
in some vaccines?
Thimerosal
is used as a preservative in some multi-dose
vials of vaccines to prevent contamination.
Preservatives are not required for
vaccines in single-dose vials. As a
preservative, thimerosal is added at
the end of the production process to
the bulk or final container to prevent
contamination after multi-dose vials
are opened. Until 1999, vaccines given
to infants to protect them against
diphtheria, tetanus, pertussis, Haemophilus
influenzae type b (Hib), and Hepatitis
B contained thimerosal as a preservative.
Today, with the exception of some flu
vaccines, none of the vaccines used
in the U.S. to protect preschool aged
children against 12 infectious diseases
contain thimerosal as a preservative.
Thimerosal still may be used in the
early stages of manufacturing of certain
vaccines, but is removed through a
purification process, with only trace,
or insignificant, amounts remaining.
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If
thimerosal was used in vaccines for
many years, why did it become a concern?
The
Food and Drug Administration (FDA)
Modernization Act of 1997 called for
the FDA to review and assess the risk
of all mercury containing food
and drugs. As part of this effort,
the FDA conducted a review of mercury
content in vaccines.
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What
recommendations did the Federal government
make in 1999 with respect to thimerosal
in vaccines?
A
review conducted by the Food and Drug
Administration (FDA) concluded that
the use of thimerosal as a preservative
in vaccines might result in the intake
of mercury during the first 6 months
of life that exceeds the Environmental
Protection Agency (EPA), but not the
FDA, the Agency for Toxic Substances
and Disease Registry (ATSDR), or the
World Health Organization (WHO) guidelines
for methylmercury intake (Ball
et al., 2001). Thimerosal contains
ethylmercury. Methylmercury
is a related compound and has been
more thoroughly researched than ethylmercury.
Thus, federal safety standards are
based on information we have about
methylmercury.
FDA’s
review found no evidence of harm caused
by doses of thimerosal in vaccines,
except for minor local reactions (Ball
et al., 2001). Nevertheless, in July
1999 the Public Health Service agencies
(PHS), the American Academy of Pediatrics
(AAP), and vaccine manufacturers agreed
that thimerosal levels in vaccines
should be reduced or eliminated as
a precautionary measure, and the Food
and Drug Administration (FDA) committed
to expediting the review of new vaccines
that do not contain thimerosal.
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What
progress has been made since July
1999 in removing thimerosal from
vaccines routinely recommended for
infants?
Substantial
progress has been made in the effort
to reduce thimerosal exposure from
vaccines. Today, with the exception
of some flu vaccines, none of the vaccines
used in the U.S. to protect preschool
aged children against 12 infectious
diseases contain thimerosal as a preservative.
The vaccines with trace amount of thimerosal
licensed to date contain less than
0.5 micrograms of mercury per dose,
that is, a given dose of vaccine contains
less than 1 part per million.
Events
that contributed to accomplishing this
goal include the licensure of a thimerosal
free Hepatitis B Vaccine (Recombinant)
manufactured by Merck and Company in
August 1999. FDA licensed another hepatitis
B vaccine with only trace amounts of
thimerosal, manufactured by GlaxoSmithKline
in March 2000. A supplement for a new
formulation of Aventis Pasteur's DTaP
Vaccine with only a trace amount of
thimerosal was approved in March 2001.
Additionally, Wyeth-Lederle Vaccines
and Pediatrics now only markets a single-dose,
thimerosal-free formulation of its
Haemophilus b (Hib) Conjugate Vaccine
in the U.S. Thus, two hepatitis B vaccines
are thimerosal free, four Hib vaccines
are thimerosal free, and two DTaP vaccines
are thimerosal free.
Prior
to the recent initiative to reduce
or eliminate thimerosal from childhood
vaccines, the maximum cumulative exposure
to mercury via routine childhood vaccinations
during the first six months of life
was 187.5 micrograms. With the newly
formulated vaccines, the maximum cumulative
exposure during the first six months
of life will now be less than three
micrograms of mercury; this represents
a greater than 98 percent reduction
in the amount of mercury a child would
receive from vaccines in the first
six months of life. [Influenza (flu)
vaccine is not given until six months
or older.]
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I’ve
heard that children may be getting
toxic levels of mercury from vaccines.
Is that true?
No.
There is no evidence of harm caused
by the minute doses of thimerosal in
vaccines, except for minor effects
like swelling and redness at the injection
site due to sensitivity to thimerosal.
Most
importantly, since 1999, newly formulated
thimerosal preservative-free vaccines
have been licensed. With the newly
formulated vaccines, the maximum cumulative
exposure during the first six months
of life will now be less than three
micrograms of mercury. No children
are receiving toxic levels of mercury
from vaccines.
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What
research is being conducted by the
Federal Government regarding the
safety of vaccines containing thimerosal?
There
is no evidence to suggest that thimerosal
in vaccines causes any health problems
in children and adults beyond local
hypersensitivity reactions (like redness
and swelling at the injection site).
However, efforts to remove thimerosal
from the U.S. vaccine supply have been
accompanied by research investigations
to better assess the potential health
effects of exposure to thimerosal containing
vaccines:
- The
National Institute of Allergy and Infectious
Diseases (NIAID) at the National Institutes
of Health (NIH) funds thimerosal research
that focuses on better understanding
of what happens to thimerosal once
it is introduced into the body and
how this compares to current knowledge
of methyl mercury pathways.
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A recent study sponsored by the
NIAID and conducted at the University
of Rochester assessed mercury levels
in 40 infants who received vaccines
containing thimerosal and 21 infants
who received thimerosal-free vaccines.
The scientists measured the level
of mercury in the infants’
blood, urine and stool up to 28
days after vaccination. They found
that 1) infants who were given
vaccines with thimerosal had levels
of mercury well below the safe
level of 29 nmol/L (this level
is set ten times lower than the
level at which mercury begins to
cause neurological problems) and
2) the body seems to be able to
get rid of thimerosal (ethyl mercury)
via the gastrointestinal tract
(stools) much quicker than it gets
rid of methyl mercury. For more
information about the different
types of mercury go to http://www.cdc.gov/nip/vacsafe/concerns/thimerosal/
faqs-mercury.htm
- NIAID
and the National Institutes of
Environmental Health Sciences (NIEHS)
are also funding studies comparing
the pharmacokinetics and tissue
distribution of thimerosal, ethyl
mercury, and methyl mercury in
non-human primates. Pharmacokinetics
is the study of how an agent is
absorbed, distributed, metabolized
(broken down), and excreted. For
more information go to
http://www.niaid.nih.gov/factsheets/thimerosal.htm
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The Food
and Drug Administration (FDA) has been
actively addressing the issue of thimerosal
as a preservative in vaccines. For
information on FDA activities related
to thimerosal and vaccines go to
http://www.fda.gov/cber/vaccine/thimerosal.htm
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- The
CDC’s Center for Environmental Health
and the National Center for Health
Statistics are doing a study looking
at all mercury exposures and working
with the National Health and Nutrition
Examination Survey (NHANES). NHANES
4 will collect samples of blood, hair
and urine from all women of reproductive
age and children under 5 in order to
assess mercury levels in the body from
all sources of mercury a person can
be exposed to in the environment. Findings
of a study conducted using NHANES 3
data to check blood and hair mercury
levels suggest that the mercury levels
in young children and in women of childbearing
age are generally below the level considered
hazardous (MMWR;50, 140-143).
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Does
thimerosal cause autism?
There
is no conclusive evidence that any
vaccine or vaccine additive increases
the risk of developing autism or any
other behavior disorder. Rather, evidence
is accumulating of lack of any harm
resulting from exposure to vaccine
containing-thimerosal as a preservative.
In a 2004 report, the Institute of
Medicine (IOM) concluded that there
is no association between autism and
vaccines that contain thimerosal as
a preservative. Nonetheless, given
the level of concern among parents
and others regarding vaccines and autism,
the CDC is committed to investigating
this issue to the fullest extent possible,
using the best scientific methods available.
For
more information on autism and vaccines
go to www.cdc.gov/nip/vacsafe/concerns/autism/default.htm
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What
about a 2003 study that claimed to
find a relationship between thimerosal
in vaccines and autism, speech disorders,
and heart disease?
In
2003, Geier and Geier reported conducting
two analyses to test whether thimerosal
in vaccines is associated with autism,
speech disorders, and heart disease.
The researchers inadequately described
the methods they used, making it impossible
to determine exactly what was done
and how the results should be interpreted.
In the first analysis, the researchers
reviewed Vaccine Adverse Event Reporting
System (VAERS) reports involving autism,
speech disorders, and heart disease.
They state that they compared VAERS
reports involving thimerosal-containing
DTP and DTaP vaccines with those involving
thimerosal-free DTaP vaccines. There
are a number of weaknesses in this
analysis, including an apparent misunderstanding
among the authors regarding VAERS reporting
requirements. VAERS is a passive surveillance
system for reporting possible vaccine
adverse events that depends on health
care providers, patients, and/or others
to file reports. Health effects reported
to VAERS as following vaccination may
be true adverse events, coincidental
occurrences, or mistakes in filing.
Because of this, VAERS has certain
weaknesses that limit the system, including
incomplete reporting, lack of verification
of diagnoses, and lack of data on those
who were vaccinated and did not report
problems. VAERS data are useful for
“hypothesis generation”
(raising questions), but should not
be used for research aimed at determining
whether vaccines cause certain health
problems as done by Geier and Geier.
Moreover, children who could have received
thimerosal-free DTaP vaccine were less
likely to have autism or speech disorders
diagnosed because they were younger
than the children in the thimerosal-containing
vaccines group. In the heart disease
evaluation, the authors examined reports
coded as “heart arrest,”
these cases in VAERS are completely
different from the coronary heart disease
cases in the studies that the authors
cite to support a possible association
between mercury and heart disease.
It is also unclear how the researchers
calculated levels of mercury exposure,
because their calculations are inconsistent
with the known levels of mercury that
were in thimerosal-containing DTP or
DTaP vaccines.
In
the second analysis, the authors looked
at the estimated amount of mercury
exposure from vaccines over time and
the number of children enrolled in
U.S. special education programs for
selected disabilities. The authors
present figures with very high correlations,
but from the limited description provided,
it does not seem that the appropriate
data were available to perform the
analyses and derive the conclusions
that the authors report. Although enrollment
in special education of children with
autism did increase during the 1990’s,
it has not been determined whether
this represents a real increase in
the incidence of autism as opposed
to increased awareness and acceptance
of the diagnosis, better recognition,
changing diagnostic criteria, or educational
and service incentives to make the
diagnosis.
The
American Academy of Pediatrics has
more information on this study at http://www.aap.org/profed/thimaut-may03.htm.
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Great
Britain experienced a rapid rise
in autism among children born in
the 1980's and early 1990's. Could
this be due to thimerosal in vaccines?
It
is unlikely that the rapid increase
in autism cases in the UK was due to
thimerosal. The only vaccine in the
UK’s childhood immunization program
that contains thimerosal is DTP. All
other vaccines (OPV, BCG, MMR, Hib,
menC) added to the program since the
1950's are and have always been thimerosal
free. In addition, if thimerosal in
vaccines were causing autism, we would
expect to see a simultaneous increase
in both thimerosal exposure
and autism cases. However, from the
1950's on, there was no increase in
the amount of thimerosal UK children
were receiving from vaccines, yet there
was a jump in autism cases in the 1980's.
A
significant change in the UK’s program
did occur in 1990 when they accelerated
their immunization schedule so vaccines
would be given earlier (changed from
3, 5, and 8 months to 2, 3 and 4 months).
However, the rate of autism was rising
long before this change occurred (see
Fombonne, 2001).
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I
understand some people are sensitive
to mercury and must avoid it. Do
they have problems with thimerosal-containing
vaccines?
Some
individuals experience local skin reactions
such as redness and swelling that may
suggest a delayed-type of minor allergic
reaction following injection with products
containing thimerosal. Research suggests
that most people who have a contact
or skin allergy to thimerosal will
not have the reaction when thimerosal
is injected under the skin (Forstrom,
1980; Jacobs 1982). A prior history
of a minor reaction to thimerosal in
a vaccine is not considered a contraindication
to further vaccination with thimerosal-containing
vaccines. Severe anaphylactic (allergic)
reaction to any vaccine is a contraindication
to further vaccination with the vaccine.
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Do
measles, mumps, and rubella (MMR)
vaccines contain thimerosal?
No,
MMR vaccine does not and never did
contain thimerosal. Varicella (chickenpox),
inactivated polio (IPV), and pneumococcal
conjugate vaccines have also never
contained thimerosal.
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Do
all flu vaccines contain thimerosal?
No.
Influenza vaccine is currently available
both with thimerosal as a preservative
and preservative-free. For the 2004-05
influenza season, it is likely that
6-8 million doses of inactivated influenza
vaccine without thimerosal as a preservative
will be available. This represents
a substantial increase in the available
amount of inactivated influenza vaccine
without thimerosal as a preservative,
compared with about 3.2 million doses
that were available during the 2003-04
influenza season.
The
removal of thimerosal as a preservative
from influenza vaccine is a complicated
process. The total amount of flu vaccine
without thimerosal as a preservative
will be increased as vaccine manufacturing
capabilities are expanded. In the meantime,
it is important to keep in mind that
the benefits of influenza vaccination
outweigh the theoretical risk, if any,
for exposure to thimerosal. Each year,
an average of about 36,000 people in
the United States die from influenza,
and 114,000 have to be admitted to
the hospital as a result of influenza.
People age 65 years and older, people
of any age with chronic medical conditions,
and very young children are more likely
to get complications from influenza.
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Why
are chemicals and other substances
added to vaccines?
Many
foods and medicines, including vaccines,
have chemicals added to them to prevent
the growth of germs, reduce spoilage,
and prevent it from losing its potency
over time.
Some
additives are used in the production
of vaccines. Vaccines may include suspending
fluid (e.g., sterile water, saline,
or fluids containing protein); preservatives
and stabilizers (e.g., albumin, phenols,
and glycine); and adjuvants, or enhancers,
that help the vaccine improve its immunogenicity
(ability to protect against disease).
For
more information on additives, go to:
http://www.cdc.gov/nip/vacsafe/concerns/gen/additives.htm
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How
can I find out what chemical additives
are in specific vaccines?
Ask
your healthcare provider or pharmacist
for a copy of the vaccine package insert.
The package insert lists ingredients
in the vaccine and discusses any known
adverse reactions. |
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