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 treatment that can be expected to influence immune response. Such treatment includes, but is not limited to, systemic or high dose inhaled (\>800µg/day of beclomethasone dipropionate or equivalent) corticosteroids, radiation treatment or other immunosuppressive or cytotoxic drugs * Have had severe allergic reactions or anaphylaxis since the second vaccination in Study 810501 * Have a rash, dermatologic condition or tattoos which may interfere with injection site reaction rating * Have undergone systemic corticoid therapy within 30 days prior to study entry * Have a functional or surgical asplenia * Have a known or suspected problem with alcohol or drug abuse * Were administered an investigational drug within six weeks prior to study entry or are concurrently participating in a clinical study that includes the administration of an investigational product * Are a member of the team conducting this study or are in a dependent relationship with the study investigator. Dependent relationships include close relatives (i.e., children, partner/spouse, siblings, parents) as well as employees of the investigator If female, are pregnant or lactating