Recently, a class action lawsuit was filed seeking to force several pharmaceutical companies to investigate whether the mercury containing preservative thimerosal, a one time common ingredient in childhood vaccines, causes autism and other brain damage in children. Thimerosal is no longer used in vaccines; however, vaccines produced before the use of the preservative was banned remain on the shelves.

In 1997 the Food and Drug Administration (FDA) ordered drug companies to reveal how much thimerosal they included in their vaccines. Reports indicate that the resultant studies shocked FDA officials, as the levels of mercury found in many of the pediatric vaccines exceeded levels considered safe for adults.