There is general agreement that autism is a very complex disorder that undoubtedly has many causes. The M.I.N.D. Institute is committed to an open-minded approach that supports research on a broad spectrum of factors that might lead to autism. Because autism is often diagnosed around the time that children are receiving their vaccinations against diseases such as measles, many parents have worried that vaccines are actually causing their children’s autism. The Measles, Mumps and Rubella (MMR) vaccine has received substantial attention both in the scientific and parental communities and in the popular press.

Large scale epidemiological studies in Denmark have shown that the children vaccinated with the MMR vaccine are at no greater risk of autism than children who are not vaccinated (Madsen, Hviid et al. 2002). The literature on this topic has been reviewed by many immunologists and there appears to be little support for the idea that the MMR vaccine causes autism in the general population (Borchers, Keen et al. 2002; Elliman and Bedford 2002; Rall 2003). Further, measles is a known deadly disease. In fact, worldwide, it continues to be the fifth largest cause of death in children under five years of age (Strebel, Cochi et al. 2003). One is forced to conclude that current research and knowledge does not suggest that vaccines are a cause of autism spectrum disorders, and that vaccinations in healthy children are safe and very important in preventing the re-emergence of epidemics of infectious diseases that have killed millions of people in the past.

Does this mean that we can say without a doubt that vaccines do not cause autism in some children? The answer to this question is “no”. There is emerging evidence that some children are immunologically compromised and therefore may respond in an atypical way to vaccinations. We do not currently understand how atypical immune responses might influence the developing nervous system or how commonly such adverse effects occur. Further, we currently have no way to identify those children who might respond adversely to vaccines. Several research projects at the M.I.N.D. Institute are attempting to find such diagnostic markers. Clearly more research needs to be carried out on the relationship between the immune system and autism. Practically, if your child has clinical indications of an immune system abnormality, such as unusual or difficult to treat infections, or your family has a long and extensive history of immunological problems, we recommend that you consult with your physicians about the safest options for immunizing your children.

A topic related to vaccines is the role of mercury as a cause of autism, particularly the role of the preservative thimerosal that was in some pediatric vaccines, but not MMR. There is no doubt that mercury, in a variety of forms, is neurotoxic (Costa, Aschner et al. 2004; Davidson, Myers et al. 2004). The level of mercury that is “safe” to the developing nervous system has not been determined. Again, large scale epidemiological studies have demonstrated that the amount of thimerosal received by children during the course of their vaccinations is not associated with higher risks of autism to the general population (Madsen, Lauritsen et al. 2003). However, a recent study carried out by Mady Hornig, M.D., and colleagues (Hornig, Chian et al. 2004), which was funded, in part, by the M.I.N.D. Institute, has raised the possibility that certain strains of mice with immune dysfunction may be particularly susceptible to the neurotoxic effects of thimerosal. Some of the mice in Dr. Hornig’s study were healthy and pediatric levels of thimerosal did not affect either their behavior or brain development. However, in an inbred strain of mice that is prone to autoimmune problems, treatment with the same pediatric levels of thimerosal led to both behavioral problems and abnormal development of certain brain regions. These findings will, of course, need to be independently replicated. But, they suggest that more research must be focused on detecting which individuals are genetically vulnerable to environmental challenges such as mercury, PCBs and others.

The M.I.N.D. Institute supports the removal of thimerosal from all vaccines, and encourages parents to specifically request that the vaccines given to their children be thimerosal free. There are alternative methods for preservation and all of the standard pediatric vaccines are currently available without thimerosal. Given the uncertainty about the toxicity of mercury, it is only prudent to eliminate the exposure of infant children to this toxicant. There are, however, other sources of mercury, for example, from thimerosal in consumer products (http://www.fda.gov/cder/fdama/mercury300.htm) and from organic mercury in fish. Again, it becomes critical to determine what, if any, level of mercury exposure is safe to the developing infant. Ongoing studies at the Center for Children’s Environmental Health at UC Davis and the M.I.N.D. Institute are addressing this issue.

References:

Borchers, A. T., C. L. Keen, et al. (2002). "Vaccines, viruses, and voodoo." J Investig Allergol Clin Immunol 12(3): 155-68.

Costa, L. G., M. Aschner, et al. (2004). "Developmental neuropathology of environmental agents." Annu Rev Pharmacol Toxicol 44: 87-110.

Davidson, P. W., G. J. Myers, et al. (2004). "Mercury exposure and child development outcomes." Pediatrics 113(4 Suppl): 1023-9.

Elliman, D. A. and H. E. Bedford (2002). "Measles, mumps and rubella vaccine, autism and inflammatory bowel disease: advising concerned parents." Paediatr Drugs 4(10): 631-5.

Hornig, M., D. Chian, et al. (2004). "Neurotoxic effects of postnatal thimerosal are mouse strain dependent." Mol Psychiatry.

Madsen, K. M., A. Hviid, et al. (2002). "A population-based study of measles, mumps, and rubella vaccination and autism." N Engl J Med 347(19): 1477-82.

Madsen, K. M., M. B. Lauritsen, et al. (2003). "Thimerosal and the occurrence of autism: negative ecological evidence from Danish population-based data." Pediatrics 112(3 Pt 1): 604-6.

Rall, G. F. (2003). "Measles virus 1998-2002: progress and controversy." Annu Rev Microbiol 57: 343-67.

Strebel, P., S. Cochi, et al. (2003). "The unfinished measles immunization agenda." J Infect Dis 187 Suppl 1: S1-7.