Claims that autism is caused by vaccines containing thiomersal have been floored by increasing rates of autism in children not exposed to the chemical.

No link has been found between autism spectrum disorders (ASD) and a mercury-containing compound known as thiomersal that is used in some vaccines. Nevertheless, since 2000, thiomersal has been phased out of most paediatric vaccines in the US. Now a report published by the US Centers for Disease Control and Prevention shows that, despite this, the prevalence of ASD has continued to grow.

The data, from 13 areas in the US, reveal that in 2008, 11.4 kids aged eight per 1000 had an ASD compared with 6.4 per 1000 in 2002 - a 78 per cent increase. "Since the [latest data] came from kids who had vaccines [largely] without thiomersal, this factor plays no apparent role in the increased rates of the disorder," says Emanuel DiCicco-Bloom of the Robert Wood Johnson Medical School in Piscataway, New Jersey, who was not involved in the study.