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JOINT STATEMENT CONCERNING REMOVAL OF THIMEROSAL FROM VACCINES FROM
•AAFP - The American Academy of Family
Physicians,
•AAP - The American Academy of Pediatrics,
•ACIP - The Advisory Committee on Immunization Practices,
•PHS - The United States Public Health Service
Approved on June 22, 2000
INTRODUCTION
BACKGROUND
PROGRESS
REPORT ON VACCINE SUPPLY
PROGRESS
REPORT ON RESEARCH
POLICY
SUMMARY
INTRODUCTION
This statement has been prepared by the American Academy of Family
Physicians, the American Academy of Pediatrics, the Advisory Committee on
Immunization Practices, and the U.S. Public Health Service in response to 1)
the progress being made in achieving the national goal declared in July 1999
to remove thimerosal from vaccines, and 2) the results of studies to better
assess any potential relationship between exposure to mercury in thimerosal
containing vaccines and health effects.
BACKGROUND
A Joint Statement issued by AAP and the PHS in July 1999 and agreed to by the
AAFP later in 1999 established the goal of removing the vaccine preservative
thimerosal as soon as possible from vaccines routinely recommended for
infants. Thimerosal is a derivative of ethylmercury and has been used as an
additive to biologics and vaccines since the 1930s because it is effective in
killing bacteria and in preventing bacterial contamination, particularly in
opened multi-dose containers. While there was no evidence of any harm caused
by low levels of thimerosal in vaccines and the risk was only theoretical,
this goal was established as a precautionary measure. There is public concern
about the health effects of mercury exposure of any sort, and the elimination
of mercury from vaccines was judged a feasible means of reducing an infant's
total exposure to mercury in a world where other environmental sources of
exposure are more difficult or impossible to eliminate (e.g. certain foods).
PROGRESS REPORT ON VACCINE SUPPLY
During the year since the original statement, substantial progress has been
made in removing thimerosal from vaccines. A hepatitis B vaccine without
thimerosal produced by Merck Vaccine Division was released in August 1999,
and in March 2000 a hepatitis B vaccine that does not contain thimerosal as a
preservative was approved for SmithKline Beecham Biologicals. This SKBB
product contains only a trace amount of mercury (less than 0.5mcg/dose), a
greater than 96% reduction from the 12.5mcg in the previous SKBB vaccine and
an amount considered clinically insignificant. A combination vaccine
containing both hepatitis B and Haemophilus influenzae type b (Hib) vaccine produced
by Merck Vaccine Division, Inc. has always been free of thimerosal. Thus, as
of March 2000, all U.S children had access to hepatitis B vaccines that are
free of thimerosal as a preservative.
In addition, three of the four Hib vaccines currently licensed for use in the
United States do not contain thimerosal as a preservative. The fourth vaccine
is produced by Wyeth Lederle which has marketed this Hib vaccine in both
thimerosal free, single dose formulations and multidose,
thimerosal-containing preparations. As of July 2000, Wyeth Lederle is
expected to produce only the single dose, thimerosal-free formulation for the
U.S. Thus, the Hib vaccine supply being produced will become entirely free of
thimerosal as a preservative beginning in July 2000.
For DTaP vaccine, a thimerosal free vaccine produced by SKBB has been
licensed and available in the United States since 1997. There are three other
vaccine manufacturers whose DTaP vaccines still contain thimerosal as a
preservative. Discussions are underway with these manufacturers and it is
hoped that at least one additional DTaP vaccine without thimerosal as a
preservative will become available in early 2001.
Based on this progress, the most likely maximum amount of ethylmercury that
an infant may be exposed to from the routine immunization schedule has been
reduced by 60% from 187.5mcg to 75mcg. Measles mumps rubella, varicella,
inactivated polio, and pneumococcal conjugate vaccines have never contained
thimerosal.
PROGRESS REPORT ON RESEARCH
Since July 1999, efforts to remove thimerosal from the US vaccine supply have
been accompanied by research investigations to better assess the potential
health effects of exposure to thimerosal-containing vaccines.
First, NIH scientists are collaborating with investigators from the
University of Rochester and the Bethesda Naval Hospital to determine
retrospectively the blood levels of mercury achieved following routine
pediatric vaccination. Preliminary data from a very small number of term
infants in these studies indicate that the blood levels of mercury produced
by exposure to thimerosal preservative containing vaccines are less than
2mcg/L, the level many experts consider as background.
These findings differ from those recently reported by Stajich and coworkers
(J Pediatr 2000;136:679-681) who found blood mercury levels of greater than
2.9 mcg/L in 9 of 15 premature infants who had received a hepatitis B
immunization within the first week of life. However, all of these infants
were very premature (birth weights < 1000 grams, mean birth weight of 748
grams). Hepatitis B immunization is not recommended for infants < 2000
grams unless their mother is HBsAg positive.
Second, CDC is using large automated databases that link vaccination and
International Classification of Disease codes (ICD-9) stored in medical
records in managed care organizations (the Vaccine Safety Datalink project,
VSD) to rapidly screen for any possible association between exposure to
thimerosal containing vaccines and a variety of neurologic, developmental,
and renal outcomes.
In the preliminary screening phase of this investigation, CDC and VSD
investigators observed no association between exposure to thimerosal
containing vaccines and 12 of the 17 renal and neurologic ICD-9 codes
examined from two of the managed care organizations studied. These 12 ICD-9
codes examined were extrapyradimal disease, autism, childhood psychosis,
stammering, sleep, eating, misery disorders, mixed emotional conditions,
infantile cerebral palsy, epilepsy, migraines, and unspecified renal
conditions. From these preliminary data, an inconclusive correlation (i.e.,
one that is inadequate to support or refute a causal link) was observed
between exposure to thimerosal containing vaccines and five of the 17 ICD-9
codes, including language delays, speech delays, attention deficit disorder,
unspecified developmental delays and tics. There was no evidence of any
increased risk for these codes among premature infants.
Reviews of these preliminary observations by expert consultants first at CDC
and then from outside PHS identified many important shortcomings in the
dataset and in this type of analytic approach. These consultants concluded
that the correlation is very weak and insufficient to support a causal
relationship. This inconclusive information does not provide a sound
scientific basis for making new policy decisions or changes in current
policies. Nevertheless, because of the potential implications of this
screening-phase observation, consultants urged further investigation.
In pursuit of these further studies, CDC investigators have obtained
preliminary data from a third managed care organization. Analyses of these
data using the same methods and having similar limitations as in the two
earlier managed care organizations showed no association for two specific
conditions, namely, speech delay, which in this dataset included language
delay, and attention deficit disorder. The number of events was too small to
examine the association with tics and the category of unspecified
developmental delays was not defined clearly enough to permit reanalysis.
Additional review of this dataset is planned and new studies which can test
the hypotheses of interest more directly and definitively also are being
considered by CDC.
POLICY
The AAFP, AAP, and the PHS in consultation with the ACIP reaffirm the goal
set in July 1999 to remove or greatly reduce thimerosal from vaccines as soon
as possible for the following reasons: 1) the removal or substantial
reduction of thimerosal from vaccines is feasible, 2) the progress in removal
which has been made to date is substantial, 3) the discussions between the
Food and Drug Administration and the vaccine manufacturers in removing
thimerosal are ongoing, and 4) the public concern about the use of mercury of
any sort remains high. Based on information from the FDA and manufacturers,
the PHS projects that the United States will complete its transition to a
secure routine pediatric vaccine supply free of thimerosal as a preservative
(i.e. at least two vaccine products each for Hep B, Hib, and DTaP) by the
first quarter of 2001.
The use of any Hib or DTaP vaccine should continue according to the currently
recommended schedule. The risk of not vaccinating children on time with DTaP
to protect them against pertussis or with any remaining Hib vaccine is
believed to far outweigh the risk, if any, of exposure to thimerosal
containing DTaP and Hib vaccines which are still available or still being
produced. Any new information from ongoing investigations will be monitored
carefully by the PHS to determine if any change in this assessment and in
existing recommendations is warranted.
Other vaccines such as diphtheria-tetanus, meningococcal, and influenza
vaccines will still contain thimerosal after the first quarter of 2001.
Diphtheria-tetanus (DT) and meningococcal vaccines are not recommended for
children as part of the recommended childhood immunization schedule.
Influenza vaccine is not recommended routinely for infants under 6 months of
age, but should be given to infants and children 6 months of age and older
who are at high risk of morbidity and mortality from the influenza virus.
Continued use of these products as indicated is recommended until thimerosal
is removed or until new products without thimerosal are licensed.
The vaccination of children in much of the world will continue to require the
use of multi-dose vials for reasons of cost, production, and storage
capacity. Multi-dose vials require a preservative to prevent microbial
contamination after the vial is opened. While thimerosal is currently the
preferred preservative, manufacturers are encouraged to seek alternatives.
SUMMARY
In 1999, family physicians, pediatricians, federal health officials, and
vaccine manufacturers stated that because any potential risk from mercury is
of concern, and the elimination of exposure to mercury in the
form of thimerosal from vaccines is feasible, thimerosal should be removed
from vaccines as soon as possible. However, there remains no convincing
evidence of harm caused by low levels of thimerosal in vaccines.
Since mid-1999, two new hepatitis B vaccine products have been introduced and
one new Hib product will be produced next month to make the new supply of
both hepatitis b and Hib vaccines for infants entirely free of thimerosal as
a preservative. One of the four licensed DTaP vaccines is already thimerosal
free, and at least one other thimerosal free DTaP vaccine is anticipated to
be licensed by early 2001. Thus, the likely maximum number of micrograms of
ethylmercury that an infant may be exposed to from the routine immunization
schedule will have been reduced by 60%. This amount will be reduced even
further in early 2001 when at least two vaccine products for hepatitis B,
Hib, and DTaP are expected to be available. Meanwhile, research on the
potential health effects of exposure to thimerosal is continuing, and
information will be monitored closely by the PHS to determine if any changes
in policy are needed.
The AAFP, AAP, ACIP, and the PHS recommend continuation of the current policy
of moving rapidly to vaccines which are free of thimerosal as a preservative.
Until an adequate supply of each vaccine is available, use of vaccines which
contain thimerosal as a preservative is acceptable.
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