- Presence of the following serious and active medical conditions: demyelinating or progressive degenerative disorders; central nervous system infection; progressive degenerative neurological disorder; ischemic heart disease; respiratory, renal, or liver disease; Type I diabetes; malignant neoplasm; hyper- or hypo-coagulopathy; Acquired Immune Deficiency Syndrome (AIDS); or seizure disorder. Participants with a history of more than two febrile seizures prior to 1 year of age are eligible.