- Within 14 days of initial symptoms of present illness diagnosed by a health care provider as infectious mononucleosis and confirmed to be due to primary EBV by antibody profile. The criteria for antibody confirmation of primary EBV at the screening visit are: 1)Positive for anti-EBV VCA IgM antibody and negative for anti-EBV EBNA1 IgG antibody; 2)EBV antibody testing will be done in the Clinical Virology Research Laboratory using commercial ELISA kits (Diamedix Corporation, Miami, FL).