There is absolutely no evidence of any adverse effects of thimerosal in vaccines, and the EPA's precautionary limit is below the level that the Food and Drug Administration considers dangerous. The concern arises in part from a health disaster of the 1950s, when a group of pregnant Japanese women ate mercury-contaminated fish. The women themselves developed few problems, but some of their babies were born retarded, blind and deaf due to mercury exposure in the womb. If you have not heard about the AAP's recommendation, it's likely you have heard the clamor that has resulted from it. Some groups have seized upon this development to claim that it validates their long-held concerns about vaccine safety.
Some parents say that a vaccine caused a particular illness in their children.
While anything is possible, it is far more likely that the autism resulted from other, unknown, causes. The MMR vaccine is given after 12 months of age. Autism is often first detected in children between one and two years of age. However, the close proximity in time does not demonstrate that the vaccine caused the developmental problem. The largest and best-done study to date showed no evidence of a connection.