 1. To evaluate the safety of the administration of one or two priming 0.5mL intramuscular IM doses of an MF59-adjuvanted AVietnam11942004 H5N1 Clade 1 influenza vaccine each dose containing 7.5μg of H5N1 haemagglutinin, in immunologically naïve subjects, followed by one 3.75μg or 7.5μg booster dose of antigenically drifted MF59-adjuvanted H5N1 vaccine, or non-adjuvanted antigenically drifted H5N1 vaccine. 