Searching for the Missing Link

Mon Mar. 1, 2004 3:00 AM EST

Both sides of the thimerosal-autism debate have cited medical and scientific findings that appear to support their positions and refute their opponents'. Without a definitive, independent large-scale study of American children, the battle promises to drag on. In the meantime, critics continue to attack research on both sides for flaws such as small sample sizes, sloppy analyses, and conflicts of interest. Here are some of the recent reports and studies commonly cited by both sides:


"Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children"
A. J. Wakefield, S. H. Murch, A. Anthony, J. Linnell, D. M. Casson, M. Malik, M. Berelowitz, A. P. Dhillon, M. A. Thomson, P. Harvey, A. Valentine, S. E. Davies, and J. A. Walker-Smith
The Lancet, February 1998

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The authors of this study [registration required] suggested that the measles-mumps-rubella (MMR) vaccine might cause autism and inflammatory bowel disease in children. The editor of The Lancet recently accused the study's lead author of a conflict of interest due to his undisclosed work with families who believe their children were injured by vaccines.


"Immunization Safety Review: Measles-Mumps-Rubella Vaccine and Autism"
Kathleen Stratton, Alicia Gable, Padma Shetty, and Marie McCormick
Institute of Medicine, April 2001

This report found no association between the mumps-measles-rubella (MMR) vaccine and autism. The authors cautioned that if a small number of children predisposed to adverse reactions suffered neurological damage due to the vaccine, previous studies "may not have sufficient precision" to detect them.


"Autism: A Unique Type of Mercury Poisoning"
Sallie Bernard, Albert Enayati, Teresa Binstock, Heidi Roger, Lyn Redwood, and Woody McGinnis
Medical Hypotheses, April, 2001

The authors of this study compared the common characteristics of autism with those of mercury poisoning. Some children may be predisposed to develop autism after receiving vaccines containing thimerosal, they wrote. They concluded that the mercury in thimerosal is "causing a heretofore unrecognized mercurial syndrome" in autistic children.


"Immunization Safety Review: Thimerosal-Containing Vaccines and Neurodevelopmental Disorders"
Kathleen Stratton, Alicia Gable, and Marie C. McCormick
Institute of Medicine, October 2001

This IOM report found insufficient evidence to accept or reject a causal relationship between thimerosal-containing vaccines (TCVs) and neurological disorders, but said the "hypothesis is biologically plausible." The authors recommended that "full consideration be given… to removing thimerosal from vaccines administered to infants, children or pregnant women in the United States."


"Mercury concentrations and metabolism in infants receiving vaccines containing thimerosal: a descriptive study"
Michael Pichichero, Elsa Cernichiari, Joseph Lopreiato, and John Treanor
The Lancet, November 2002

This study [registration required] measured mercury levels in blood, stool, and urine samples from infants soon after being vaccinated with TCVs. Finding low concentrations of mercury in blood, and higher concentrations in stool, it concluded that thimerosal "poses very little risk to full-term infants." Safe Minds suggested that the authors' connections to vaccine manufacturers "may have resulted in a biased study design and biased interpretation of the results."


"Thimerosal and Autism?"
Karin Nelson and Margaret Bauman
Pediatrics, March, 2003

In this review of existing research, the authors concluded that a thimerosal-autism link is "improbable."


"Toxicity of Thimerosal"
David Baskin, Hop Ngo, and Vladimir V. Didenko
Society of Toxicology, May 2003

After immersing skin and brain cells in thimerosal, the authors found it damaged DNA and cell structures, sometimes killing the cells.


"Neurodevelopmental Disorders after Thimerosal-Containing Vaccines: A Brief Communication"
Mark Geier and David Geier
Experimental Biology and Medicine, June 2003

Using data obtained from the CDC's Vaccine Adverse Events Reporting System (VAERS) the authors compared [links to PDF] the occurrence of neurodevelopmental disorders amongst children reporting adverse reactions who received thimerosal-containing diphtheria, tetanus, and pertussis (DTaP) vaccinations with that of those who received thimerosal-free versions of the same vaccine. Finding a significantly higher risk for autism after receiving thimerosal-containing DTaP, they recommended that manufacturers consider removing thimerosal from all vaccines. The American Academy of Pediatrics criticized the study for "conceptual and scientific flaws, omissions of fact, inaccuracies, and misstatements."


"Reduced Levels of Mercury in First Baby Haircuts of Autistic Children"
Amy S. Holmes, Mark F. Blaxill, and Boyd E. Haley
International Journal of Toxicology, July-August 2003

Samples from the first haircuts of 94 autistic children showed lower levels of mercury than non-autistic children's. The authors found that the autistic children's mothers had been exposed to higher levels of mercury through Rho D immunoglobulin and amalgam dental fillings. They suggested that exposures to mercury in utero and in infancy could increase the risk of autism.


"Association Between Thimerosal-Containing Vaccine and Autism"
Anders Hviid, Michael Stellfeld, Jan Wohlfahrt, and Mads Melbye
Journal of the American Medical Association, October 2003

The authors looked at autism rates before and after Denmark stopped using TCVs in 1992 (it was the first country to do so). The study of 467,000 Danish children over 31 years found no decrease in autism rates after 1992. It concluded that there is no causal relationship between thimerosal and autism. A Safe Minds response said the study was "full of flaws and inaccuracies."


"Safety of thimerosal-containing vaccines: a two-phased study of computerized health maintenance organization databases"
Thomas Verstraeten, Robert L. Davis, Frank DeStefano, Tracy A. Lieu, Philip H. Rhodes, Steven B. Black, Henry Shinefield, and Robert T. Chen
Pediatrics, November, 2003

Researchers analyzed CDC records and found that in over 100,000 children vaccinated during the 1990s there was "[n]o consistent significant associations… between TCVs and neurodevelopmental outcomes." Safe Minds accused the lead researcher of altering "the data, sampling and methodology of the study so that results would point to enough inconsistencies to cast doubt that mercury in vaccines causes autism."


"Activation of methionine synthase by insulin-like growth factor-1 and dopamine: a target for neurodevelopmental toxins and thimerosal"
M. Waly, H. Olteanu, R. Banerjee, S. Choi, J. B. Mason, B. S. Parker, S. Sukumar, S. Shim, A. Sharma1, J. M. Benzecry, V. Power-Charnitsky, and R. C. Deth
Molecular Psychiatry, January 2004 The authors found that thimerosal interfered with normal brain function and development.

- Rina Palta

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