Immunization Science

Autism and Thimerosal: a Danish Study

The article

Thimerosal and the Occurrence of Autism: Negative Ecological Evidence from Danish Population-Based Data. Madsen KM, Lauritsen MB, Pedersen CB, Thorsen P, Plesner A, Andersen PH, and Mortensen PB. Pediatrics 2003;112: 604-6.

The question

Did the incidence of autism in Denmark decrease after thimerosal-containing vaccines were discontinued in 1992?

The study

Thimerosal-containing vaccines were used in Denmark from the early 1950s until 1992—when thimerosal was removed from vaccines. If thimerosal-containing vaccines were causing autism in Danish children, the removal of thimerosal from vaccines should have impacted the incidence of autism.

To see if that was the case, the researchers analyzed data on autism cases from the Danish Psychiatric Central Research Register dating back to 1971.

The findings

From 1971 to 2000, 956 children were diagnosed with autism, with a rise in the number of cases in the 1990s. They found no correlation between thimerosal-containing vaccines and autism. The incidence [number of new cases over a time period] of autism remained fairly stable until 1990 and thereafter increased throughout the study period, including the period when thimerosal was no longer in vaccines.

Their data do not suggest a cause-and-effect relation between thimerosal-containing vaccines and autism.

The relevance/bottom line

This study adds to the evidence that thimerosal-containing vaccines do not cause autism.

NNii’s comment

The findings in this study should provide additional reassurance to families and others that there continues to be no scientific evidence of a relationship of autism with thimerosal in vaccines.