With the removal of thimerosal — a mercury-containing preservative — from most pediatric vaccines, the number of autism cases in California did not decrease. The findings, published in the January Archives of General Psychiatry, suggest that thimerosal in vaccines may not be associated with autism, as some parent advocacy groups have alleged in a lawsuit.
[See Neurology Today's “Federal Vaccine Court Opens Controversial Autism Proceedings,” July 3, 2007.]
Experts said the latest data are consistent with previous scientific evidence. But they noted it is not likely to end the controversy among parents with autistic children. As research into autism continues, the public needs to be made aware of the mounting evidence, they said, and physicians need to assure parents of the general importance of vaccinations for children.
Autism expert Nancy Minshew, MD, professor of psychiatry and neurology at the University of Pittsburgh, who was not involved with the current study, emphasized the urgent need for public awareness and education regarding the safety of immunization. She suggested that the Institute of Medicine (IOM) publish an accessible summary for the public, and that the press broadcast the findings responsibly.
In the current study, Robert Schechter, MD, and Judith K. Grether, PhD, of the California Department of Public Health examined data from the California Department of Developmental Services. They found that the prevalence of children (ages 3 to 12) with autism in California increased from 1995 through March 2007 — even after the discontinuation of thimerosal in vaccines. Prevalence among children ages 3 to 5 increased from January 1995 (0.6 per 1,000 live births) through March 2007 (4.1 per 1,000 live births).
Thimerosal, a preservative containing 49.6 percent ethylmercury, was eliminated from most childhood vaccines by 2001. The only routinely recommended vaccines given to young children that still contain trace amounts of thimerosal are some formulations of influenza vaccine. However, some licensed formulations are thimerosal-free, said Melinda Wharton, MD, deputy director of the National Center for Immunization and Respiratory Diseases at the CDC.
Judy Van de Water, PhD, associate professor of internal medicine at the University of California-Davis, said that in many cases of autism, the child has not been vaccinated and it is then clear that thimerosal is not the cause. She noted that it is too early to determine whether children who are susceptible to autism are particularly sensitive to mercury exposure.
“However, I do feel that it was beneficial to remove thimerosal from vaccines just to minimize exposure to mercury in general,” because it is a heavy metal and excess exposure to several heavy metals causes changes in both neurological and immune development, she said.
Dr. Wharton, of the CDC, suggested that physicians direct parents to the “Learn the Signs. Act Early” campaign from the National Center for Birth Defects and Developmental Disabilities, at: www.cdc.gov/ncbddd/autism/ActEarly/ default.htm.