Newslocale.org, Theresa Maher
Published September 26, 2007
The link between vaccines containing mercury and the development of autism and other neurological problems has been debated for a long time. Many studies have disputed the existence of this link. A new study by researchers at the US Centers for Disease Control and Prevention finds thimerosal, a mercury-containing vaccine preservative, to be relatively safe in children.
Thimerosal is a preservative in vaccines that contains 49 percent ethyl mercury. Mercury is a known neurotoxin or in other words is a chemical that causes untold harm to the brain, especially a child's developing brain.
Scientists thought that autism might be one such toxic manifestation of mercury in vaccines. In 2002, thimerosal was phased out of childhood immunizations mainly because the Public Health Service and the American Academy of Pediatrics advocated it.
The current study did not examine specific links between mercury containing vaccines and autism, but it looked at neurological problems. It involved 1,047 children who were exposed to varying levels of thimerosal during the 1990s. The children were from four HMOs (health maintenance organizations) taking part in the Vaccine Safety Datalink at CDC and were perfectly normal at the start of the study.
Exposure to thimerosal was calculated at birth, during first 28 days after birth and during the first seven months of life. Additionally researchers examined the vaccination and medical records and conducted interviews with parents and teachers in order to determine if the child had nervous tics, stuttering or problems in attention span.
The researchers subjected the children to 42 neurological tests to examine if thimerosal had any impact on their brains. Speech, motor co-ordination, intelligence and language skills were also tested.
Reporting in the September 27 issue of the New England Journal of Medicine, the researchers said that they were unable to find credible links between thimerosal and ne\urological issues although boys exposed to mercury early on did seem to have excessive tics.
William Thompson, a CDC epidemiologist, was the lead researcher of this study and he is also leading a separate study on whether thimerosal exposure causes autism.
Autism-vaccine links emerged in the late 1990s when the State of California released a report suggesting a 273 percent increase in the number of persons with autism between 1987 and 1998, the New York Times reports.
In 2004, the Institute of Medicine examined data on links between vaccines containing mercury and the incidence of autism and found no evidence linking thimerosal to autism. The Institute of Medicine's panel based its conclusions on five large studies conducted in United States, Denmark, Sweden and Britain in 2001. These studies examined thousands of children, but failed to find any link between autism and thimerosal.
The IOM report said it was an undisputed fact that high doses of mercury did cause substantial neurological damage. However no symptoms resembled that of autism, the report suggested. It added that genetics was the main causative factor as many studies had noted that autism started prenatally.
A review by the Environmental Working Group suggested that autistic children had a biomarker that rendered them susceptible to mercury and heightened their risk of developing the neurological disorder. The report cited a study by Dr. Jill James of the University of Arkansas School of Medicine, which found that children with regressive autism had high levels of oxidative stress, which made it hard for their bodies to get rid of mercury.
The study cited the following factors as well (as available on
www.ewg.com)
* The indisputable toxicity of mercury to the brain, particularly the developing brain (Limke 2004, Clarkson 2002, Mahaffey 1999).
* Peer-reviewed reports showing that autistic children are extremely poor at ridding their bodies of mercury as measured by mercury hair levels (Holmes 2003).
* The recent finding that autism-like symptoms are triggered by thimerosal in mice with a predisposition to autoimmunity (Hornig 2004).
* The fact that the prevalence of autism in boys is four times that in girls, and that boys have elevated incidence of damage from mercury exposure in epidemiologic studies (Vahter 2002).
The study said that it did not find a credible link between mercury in vaccines and autism, but there was sufficient evident to suggest mercury played some role.
This theory was reinforced by a study in 2006 which showed that autism cases declined when mercury was banned from vaccines. Using data from CDC’s Vaccine Adverse Event Reporting System (VAERS) and the California Department of Developmental Services (CDDS), lead authors David A. Geier, B.A. and Mark R. Geier, M.D., Ph.D found that autism rates hit a high of 800 in May 2003, but dropped to 620 in 2006.
The authors suggested that the 22 percent decline in autism cases was mainly due to the restriction of mercury in vaccines.
The current study did not examine links to autism, but looked at neurological disorders as a whole and did not find any link between mercury and such disorders.
Experts though are not ready to give thimerosal an all-clear. Sallie Bernard, executive director of SafeMinds said the study was observational only and hence was inconclusive.
These days thimerosal has been completely phased out except for some trace amounts in influenza vaccines. The main CDC study on whether it causes autism is due to be released later this year and could make the issue more clear. Until then doubts will continue to persist.
