Safety and Immunogenicity Study of a Booster Vaccination With a Non-Adjuvanted H5N1 Influenza Vaccine (Follow Up to Study 810501)

Inclusion Criteria: Subjects who participated in Study 810501 will be eligible for participation in the study if they: * Completed the Day 42 visit in study 810501 * Have an understanding of the study, agree to its provisions, and give written informed consent prior to study entry * Are clinically healthy, as determined by the Investigator's clinical judgment through collection of medical history and performance of a physical examination * Agree to keep a daily record of symptoms for the duration of the study * If female and capable of bearing children, have a negative urine pregnancy test result at study entry and agree to employ adequate birth control measures for the duration of the study Exclusion Criteria: * Have a history of vaccination with an H5N1 influenza virus since the second vaccination in study 810501 * Have had an allergic reaction to one of the components of the vaccine since the second vaccination in Study 810501 * Have been diagnosed with a significant neurological, cardiovascular, pulmonary (including asthma), hepatic, rheumatic, autoimmune, hematological, renal or metabolic disorder since the second vaccination in Study 810501 * Are unable to lead an independent life as a result of either physical or mental handicap * Suffer from any kind of immunodeficiency since the second vaccination in Study 810501 * Suffer from a disease or were undergoing a treatment within 30 days prior to the scheduled booster vaccination or are currently undergoing a form of t…