evidence: A primary concern that arose early in the investigation of vaccine safety was the exposure of infants and young children to mercury, a known toxin, through mandatory childhood immunizations. This concern had been raised as a possible underlying factor in the dramatic rise in rates of late-onset or ``acquired'' autism. The symptoms of autism are markedly similar to those of mercury poisoning. [...] ``My first concern was that it would harm the credibility of the immunization program. But gradually it came home to me that maybe there was some real risk to the children.'' [...] It is clear that inadequate scientific evidence exists to understand fully the likely damage done to a generation of children who were repeatedly exposed to significant levels of mercury through their mandatory childhood immunizations.