Despite the removal of thimerosal from childhood vaccines, a recent study shows that autism spectrum disorders (ASD) continued to rise in the state of California. Published in the journal Archives of General Psychiatry, researchers found that diagnosed cases of autism spectrum disorders, which include autism and related conditions, have been rising steadily in the last few years even though thimerosal has been removed from childhood vaccines.

Thimerosal was the subject of two prior posts (Thimerosal Goes to Court and No Link Found Between Thimerosal and Neurological Disorders). Many parents of autistic children believe that their child’s autism was caused by thimerosal, a mercury-containing preservative widely used in all childhood vaccines prior to 1999.

It wasn’t until 1999, that the U.S. Food and Drug Administration (FDA) recognized that children immunized according to the recommended childhood immunization schedule could be exposed to excessive levels of mercury based on Environmental Protection Agency (EPA) tolerance levels. As a precautionary measure, the American Academy of Pediatrics and the U.S. Public Health Service agreed that thimerosal be removed from vaccines as soon as possible. By 2001, all vaccines in the recommended infant immunization schedule for the United States contained at most trace amounts of thimerosal. Since 2003, all routinely recommended vaccines have been thimerosal-free, with the exception of influenza vaccine.

The authors analyzed data on childhood autism cases reported by the California Department of Developmental Services (DDS) from mid-1995 to mid-2006. They found that:

• For children born in 1993, the prevalence of autism at age 3 was 0.3 per 1,000 births.
• For children born ten years later, in 2003, the prevalence rate was 1.3 per 1,000 births.
• The highest estimated prevalence occurred in 2006, when 4.5 out of every 1,000 children born in 2000 were estimated to have autism.
• It is too early to calculate prevalence for ages 6 and up for children born after 2000, however, the prevalence at ages 3 to 5 years has risen steadily for each birth year since 1999.
• Thimerosal was phased out over the same period that saw a steady increase in autism among 3 to 5 year olds.
• Based on quarterly figures, the rate of autism cases among 3 to 5 year olds increased each quarter from January 1995 (0.6 per 1,000 live births) to March 2007 (4.1 per 1,000 live births).

This data led the authors to conclude, “Although our analysis of Department of Developmental Services data shows an increase in autism in California despite the removal of thimerosal from most vaccines, we support the continued quest for the timely discovery of modifiable risk factors for autism and related conditions.”

At the same time, they cautioned that the evaluation of the trends needs to continue in order to confirm their findings for the children born more recently.

In an accompanying editorial, Dr Eric Fombonne, of the Montreal Children’s Hospital, wrote that fears about childhood vaccines appear to persist even though the evidence does not warrant it.

“In the last decade, two hypotheses on autism-immunization links were raised that have had a profound impact in the field of autism research and practice and on public health at large,” he wrote.

The first hypothesis suggested a link between autism and the measles component of the triple measles-mumps-rubella (MMR) vaccine and the other suggested a link between autism and the mercury in thimerosal.

In 2004 the Institute of Medicine (IOM) issued a report that called for the rejection of both hypotheses, since then more studies have appeared that support the IOM view, which has been “independently reached by scientific and professional committees around the world,” wrote Fombonne.

Fombonne assured parents of autistic children that their children’s autism did not come about as a result of childhood vaccinations.

“Their autistic children, and their siblings, should be normally vaccinated, and as there is no evidence of mercury poisoning in autism, they should avoid ineffective and dangerous “treatments” such as chelation therapy for their children,” he wrote.