California Study: Autism Cases Rise in Spite of Vaccine Changes

California public health researchers have found that the prevalence of autism spectrum disorders in young children has risen, even after doctors stopped using a mercury-containing preservative thimerosal in the vaccines babies receive.

The study, "Continuing Increases in Autism Reported to California Developmental Services System," is published in the January 2008 issue of Archives of General Psychiatry. The journal has made the full text of the article available online http://archpsyc.ama-assn.org/cgi/content/full/65/1/19.

The study asked: Since people are concerned that the mercury preservative used in vaccines causes autism, what happened after 1999, when the government and doctors recommended the nation stop using vaccines containing thimerosal for infant inoculations such as DTP (diphtheria, tetanus and pertussis) and hepatitis B?

Instead of seeing a decrease in autism diagnoses, the state Department of Developmental Services (DDS) saw an increase in the estimated prevalence of autism cases. For each quarter from 1995 through the end of 2003, the prevalence of autism increased from 0.6 to 2.9 per 1,000 live births. (The prevalence for all developmental disabilities including autism also increased, from 5.4 to 8.9 per 1,000.)

The study authors continue: "From 2004 through March 2007, when we estimate exposure to thimerosal-containing vaccines during infancy and early childhood declined, the prevalence of children aged 3 to 5 years receiving services for autism continued to increase from 3.0 to 4.1 per 1,000 lives births."

The authors report in their conclusion:

Infants and toddlers in the United States were exposed to more of the ethylmercury-containing preservative, thimerosal, after recommendations in 1991 for universal administration of the hepatitis B virus and Hib [Haemophilus influenzae type b] vaccines.

They have been exposed to less thimerosal since at least the national recommendation in 1999 for its removal from childhood vaccines. If thimerosal exposure is a primary cause of autism, then the prevalence of autism would be predicted to decrease as young children's exposure to thimerosal has sharply decreased to its lowest levels in decades. We have instead found that the prevalence of autism in children reported to the DDS has increased consistently for children born from 1989 through 2003, inclusive of the period when exposure to TCVs [thimerosal-containing vaccines] has declined.

Moreover, since 2004, the absolute increase and the rate of increase in DDS clients aged 3 to 5 years with autism were higher than those in DDS clients of the same ages with any eligible condition, including autism. These time trends are inconsistent with the hypothesis that thimerosal exposure is a primary cause of autism in California.

Context for the California Study

This is the latest in a series of published research articles that fail to find a causal link between thimerosal and autism. There have been numerous media reports, analysis pieces, opinion articles, and books urging parents to trust the research and get their kids vaccinated.

Meanwhile, a special court in Washington is hearing a series of cases arguing that evidence shows that vaccines harmed their children and demanding compensatory damages.

But while ABC News reports today that the latest California study "may be the latest nail in the coffin of a theory that draws a link between the mercury-containing vaccine additive thimerosal and autism," the controversy is likely to continue.

The same day as the research report came out, the advocacy group SafeMinds.org, which supports research on the "potential harmful effects of mercury and thimerosal," had posted this note about the California study:

SafeMinds arrives at a different interpretation of the findings, showing that the data can equally support a primary causative role of thimerosal if autism causation is multifactorial. Vaccine components and environmental mercury, as well as other toxicants, are additional likely candidates. Deficiencies of the DDS data and imprecise thimerosal exposure assumptions make determination of the contribution of thimerosal to autism rates difficult. The increase in autism cases reported by Schechter and Grether since the 1980s highlights the urgency of the autism epidemic and the need to institute a rigorous and comprehensive environmental factors research program.