Rates of children suffering from autism in California have risen despite the removal of the preservative thimerosal from childhood vaccines in 2001, researchers say in a new study.

Researchers analyzed autism rates in young children over a 12-year period and discovered the first hard evidence that thimerosal plays no role in autism.  

“Whatever the explanation for this increase in children with autism, exposure to mercury in vaccines is not it. Vaccines with thimerosal and without have been safe and appropriate to give to our children,” said Robert Schechter, a medical officer with the California Department of Health Services and lead author of the study.

It seems that removing thimerosal from all recommended infants vaccines as a precautionary measure in March 2001 had no effect on reducing the number of children suffering from autism. The only childhood vaccines that contain more than trace amounts of thimerosal are multiple-dose vials of some flu vaccines.

A previous look on data referring of thimerosal affecting children from 2001 suggested there was a decline in autism beginning with 1994. The new data from March 2007 did not reflect such decline. Schechter and Judith K. Grether of the California Department of Public Health studied the prevalence of children with autism in California from 1995 through 2007. They discovered that the rate of all developmental disabilities increased from 504 to 905 per 1,000 live births.

“Not enough time had passed for autism in the younger children in that time period to be fully recognized. We saw with additional time, rather than going up and going down, autism rates continued to go up,” said Schechter.

These data lead researchers to believe that “there is an environmental source” linked to increased rates of autism.

“You cannot use this data to rule out thimerosal as a factor. What you can say is there may be -- and probably are -- other environmental triggers that play a role. It is probable that exposure to these other factors may be increasing,” said Sally Bernard, co-founder and executive director of SafeMinds, an organization that advocates “sensible action for ending mercury-induced neurological disorders.”

Results of the study were published Monday in the Archives of General Psychiatry, a publication of the Journal of the American Medical Association.