While individual practitioners may differ, this is the position of the College at the time written, after a review of the issue and pertinent literature.
The American College of Medical Toxicology (ACMT) is a professional society composed of
physician toxicologists who focus on the diagnosis, management of acute
and chronic adverse health effects due to medications, chemical,
occupational and environmental toxicants and biological hazards. The ACMT commends the efforts of the IOM report of Immunization Safety Review:Vaccines and Autism.
ACMT notes that the Immunization Safety Review Committee, while
comprised of many competent academicians, had none with the special
skill set of a medical toxicologist, a critical criterion when the
adverse effects of an organomercurial are being considered. The IOM is
encouraged to include medical toxicologists on committees that focus on
potential toxicologic exposures. Indeed, in the past, a medical
toxicologist has stepped forward on this issue. (2)
The IOM concludes
that the body of epidemiological evidence indicates that there is no
causal relationship between thimerosal containing vaccines and autism. The ACMT provides
the following background and comments. Thimerosal is a
mercury-containing organic compound (sodium ethylmercuric
thiosalicylate, also known as Merthiolate, Mercurothiolate) which
contains approximately 50% mercury by weight. (3) The United States
Code of Federal Regulations (CFR) requires the addition of a
preservative to multi-dose vials of vaccines. Since the 1930â€™s,
thimerosal has been widely used as a preservative in a number of
biological and drug products, to help prevent contamination from
microbes. When the Food, Drug and Cosmetic Act was passed in 1938,
thimerosal was placed on the GRAS (generally recognized as safe) list.
Thimerosal in concentrations of 0.001% (1 part in 100,000) to 0.01% (1
part in 10,000) has been shown to be effective in clearing a broad
spectrum of pathogens. Placed in perspective, a
vaccine containing 0.01% thimerosal as a preservative contains 50
micrograms of thimerosal per 0.5 mL dose or approximately 25 micrograms
of mercury per 0.5 mL dose, in the form of ethyl mercury. As the number
of vaccinations given to infants has increased, so has the cumulative
exposure to Thimerosal as the organomercurial preservative. (3)
1999, with a recognized increase in the prevalence of autism spectrum
syndromes, attention was called to thimerosal as a potential risk
factor, especially in combination with measles, mumps and rubella (MMR)
vaccination (4-9). At that time the Public
Health Service (including the Food and Drug Administration (FDA),
National Institutes of Health, and the Centers for Disease Control and
Prevention (CDC)), and the American Academy of Pediatrics (AAP) called
for the withdrawal of thimerosal from further use in vaccines targeted
for children. However, thimerosal in existing vaccine inventory was allowed to be used.
of this concern was based on methylmercury-related neurotoxicity, the
timing of vaccination during the first year of life when the
blood-brain barrier is more permeable to heavy metals, and a model that
equated intermittent exposure to ethylmercury to cumulative dosing of
methylmercury. Recent research has confirmed that the ethylmercury
component found in Thimerosal is less hazardous than methylmercury.
These are different compounds and should not be considered as
equivalent neurotoxins. Experimental conditions can be created that
result in neurological cell dysfunction (10,11) However,
current literature supports the contention that childhood vaccinations
do not deliver a sufficient dose to produce these neurological
large epidemiological studies have been completed in an attempt to
clarify the issue of childhood immunizations and the risk of
neurodevelopmental disorders. The CDC reviewed
computer-based vaccination records and ICD-9 codes of autistic spectrum
disorders for over 124,000 infants at two health maintenance
organizations (HMOs) in California. (12) In 2003, a published comparison of imputed thimerosal dose in Sweden, Denmark and the United States found no correlation with the rise in prevalence of autism spectrum disorders occurring in all three countries. (13) The
Institute of Medicine (IOM) of the National Academy of Sciences
assembled an Immunization Safety Review Committee that held hearings
and provided a series of reports, culminating in their 2004 Immunization Safety Review: Vaccines and Autism.(1)
a number of potential concerns have been raised (14) regarding the
adequacy of the IOM review (7 months, rather than one year catchment
period, and procedural issues such as cutoff age and ICD-9 diagnostic
listings), the ACMT believes that the IOMâ€™s conclusions are justified.
In fact, in conjunction with epidemiological data from Europe, Australia, and the United States, the IOM report stands as reassurance to parents concerned about the risk of previous vaccinations for their children.
the AAP and the combined Public Health Service agencies (CDC, NIH and
FDA) have taken a precautionary approach in encouraging vaccination of
infants with Thimerosal-free products when available (particularly for
the most susceptible infants - those that are very premature and
undernourished), the ACMT wishes to emphasize that these are also those
infants most at risk of vaccine-preventable diseases. The restriction
of vaccine access is inappropriate and results in real, as opposed to
theoretical, harm. (15,16)
ACMT further discourages chelation therapy in autistic children, a
practice that is not supported by clinical evidence either of mercury
toxicity or therapeutic effect, and which can have hazardous
the ACMT commends the IOM reportâ€™s conclusions encouraging research
funding to investigate adverse vaccine concerns, evaluating autistic
disorders up through a pre-school catchment age, and related
(1) Immunization Safety Review Committee: Vaccines and Autism. Institute of Medicine. National Academies Press, 2004. http://www.iom.edu/report.asp?id=20155 http://www.nap.edu/catalog;10997.html
(2) Brent J. Toxicologists and the Assessment of Risk: The Problem with Mercury. J Toxicol/Clin Toxicol 2001;30:707-710.
(3) Thimerosal in Vaccines (Mercury in Plasma-Derived Products). Center for Biologics Evaluation and Research, FDA. http://fda.gov/cber/vaccine/thimerosal.htm
(4) Madsen KM, Hviid A, Vertergaard M, Schendel D, Wohlfahrt J,
Thorsen P, Olsen J, Melbye M. A Population-Based Study of Measles,
Mumps and Rubella Vaccination and Autism. N Engl J Med 2002;19:1477-1482.
(5) Morris SAS, Bernstein HH. Immunizations, Neonatal Jaundice and Animal-Induced Injuries. Current Opinion in Pediatrics 2004;16:450-460.
(6) Newschaffer CJ, Falb MD, Gurney JG. National Autism Prevalence Trends from US Special Education. Pediatrics 2005;115:277-282.
(7) Parker SK, Schwartz B, Todd J, Pickering LK.
Thimerosal-Containing Vaccines and Autistic Spectrum Disorder: A
Critical Review of Published Original Data. Pediatrics 2004;114:793-804.
(8) Ruther M. Incidence of Autism Spectrum Disorders: Changes Over Time and Their Meaning. Acta Paediatrica 2005;94:2-15.
(9) Chez NG, Chin K. Hung PC. Immunizations, Immunology and Autism (Review). Seminars Ped Neurol 2004;11:214-217.
(10) Burbacher TM, Shen DD, Liberato N, Grant KS, Cernichiari E,
Clarkson T. Comparison of Blood and Brain Mercury Levels in Infant
Monkeys Exposed to Methylmercury or Vaccines Containing Thimerosal. Environmental Health Perspectives 2005;112:1015-1021
(11) Parran DK, Barker A, Ehrich M. Effects of Thimerosal on NGF Signal Transduction and Cell Death in Neuroblastoma Cells. Toxicol Sci 2005;86:132-140.
(12) Verstraeten T, Davis RL, DeStefano F, Lieu TA, Rhodes PH, Black
SB, Shinefield H, Chen RT. Safety of Thimerosal-Containing Vaccines: A
Two-Phased Study of Computerized Health Maintenance Databases. Pediatrics 2003;112:1039-1048. http://pediatrics.aappublications.org/cgi/content/full/112/5/1039?ijkey=ed4b4475a8522
(13) Stehr-Green P, Tull P, Stellfeld M, Mortenson PB,
Simpson D. Autism and thimerosal-containing vaccines: lack of
consistent evidence for an association. American Journal of Preventive Medicine. 2003;25(2):101-6.
(14) Verstraeten T. Thimerosal, the Centers for Disease Control and Prevention, and GlaxoSmith Kline. Pediatrics 2004;113:932 (letter). http://pediatrics.aappublications.org/cgi/content/full113/4/932
(15) Bigham M, Copes R. Thiomersal in vaccines: balancing the risk
of adverse effects with the risk of vaccine-preventable disease. Drug Safety. 2005;28(2):89-101, 2005.
(16) Elliott VS. Anti-thimerosal laws vex flu shot planners. American Medical News. 2004;49(16):1,4.
(17) Boy with Autism Dies after Chelation Therapy: 5-Year-Old Was Receiving Controversial Treatment in Doctorâ€™s Office. Associated Press. MSNBC, August 25, 2005. http://msnbc.msa.com/id/9074208
Prepared by the ACMT Practice Committee. Primary author: Tom L Kurt
Disclosure forms on file at ACMT
Last reviewed June 2006