Early Prophylaxis Immunologic Challenge (EPIC) Study

Inclusion Criteria: * Participants with severe and moderately severe hemophilia A (FVIII ≤ 2%) * Participants \< 1 year of age * Participants must have ≤ 3 exposure days (EDs) to any FVIII concentrate or FVIII-containing product used for treatment of minor bleeds (bleeds requiring no more than 2 infusions per event), or for preventative or precautionary infusions following possible injury * Participants with prior circumcision are allowed to enroll only if bleeding issues related to circumcision were the cause for the original diagnosis of hemophilia A and no more than 2 EDs of FVIII treatment were required * Adequate venous access (without need for central venous access device (CVAD)-placement) as determined by the physician * Written informed consent from legally authorized representative(s) Exclusion Criteria: * Life-threatening conditions (intracranial hemorrhage, severe trauma) or requirement for surgery at the time of enrollment * Evidence of inhibitor ≥ 0.6 Bethesda Unit (BU) in Nijmegen-modified Bethesda Assay at study start (samples may be retested using lupus-insensitive inhibitor tests to reduce the number of false positive inhibitor test results) * Inherited or acquired hemostatic defect other than hemophilia A * Any clinically significant, chronic disease other than hemophilia A * Known hypersensitivity to ADVATE or any of its constituents * Any planned elective surgery that cannot be postponed until after the first 20 EDs * Participation in the Hemophilia Inhibitor Previously Untreated Patient Study * Application of red blood cell, platelet, or leukocyte concentrates, or plasma * Administration of any medication affecting coagulation or platelet function * Systemic administration of any immunomodulatory drug (eg, chemotherapy, intravenous glucocorticoids) * Participation in another clinical study involving an investigational product (IP) or device within 30 days prior to study enrollment or during the course of this study