 The lead petitioners, the parents of Michelle Cedillo, claimed that Michelle's autism was caused by a vaccine.Theresa and Michael Cedillo contended that thimerosal seriously weakened Michelle's immune system and prevented her body from clearing the measles virus after her vaccination at the age of fifteen months.At the outset Special Master George Hastings, Jr. said "Clearly the story of Michelle's life is a tragic one," while pledging to listen carefully to the evidence.