 2. To examine the kinetics of the antibody responses to one 0.5mL booster intramuscular dose of antigenically drifted MF59-adjuvanted vaccine, or non-adjuvanted antigenically drifted vaccine, given at doses of 3.75 or 7.5μg, in subjects primed with one or two doses of an MF59-adjuvanted AVietnam11942004 H5N1 Clade 1 influenza vaccine; 