The purpose of this study is to demonstrate the effectiveness (seroprotection and seroconversion as measured by the hemagglutination inhibition [HI] assay) of an investigational Vero cell-derived, trivalent, seasonal influenza vaccine in adults 50 years of age and older. Subjects will be randomized in a double-blind fashion to receive a single intramuscular injection of either the investigational vaccine or a licensed egg-derived seasonal influenza vaccine. Blood will be drawn from all subjects for a determination of HI antibody titers on Days 0 and 21, body temperature and injection site reactions will be monitored daily for 7 days. In addition, subjects will be monitored for adverse events and rises in body temperature until Day 21 and again until Day 180.

Inclusion Criteria:

• Are 50 years of age or older on the day of screening
• Have an understanding of the study, agree to its provisions, have the ability to adhere to the provisions of the study and give written informed consent prior to study entry
• If female and capable of bearing children,have a negative urine pregnancy test result within 24 hours prior to the vaccination on Study Day 0 and agree to employ adequate birth control measures.

Exclusion Criteria:

• History of severe allergic reaction or anaphylaxis to egg protein or any other component of the Vero cell-derived influenza vaccine or the egg-derived influenza vaccine
• Oral temperature of >= 99.5°F (37.5°C) on the day of vaccination in this study (Note: Subjects meeting this exclusion criterion may be rescheduled for vaccination and study entry at a later date if certain requirements [in the study protocol] are met)
• Rash or dermatologic condition or tattoos which may interfere with injection site reaction rating
• Blood transfusion or immunoglobulins received within 90 days of study entry
• Live vaccine received within 4 weeks or inactivated vaccine or subunit vaccine received within 2 weeks of study entry
• Previous vaccination against influenza for the 2008/2009 northern hemisphere influenza season
• Functional or surgical asplenia (e.g. from a history of hemoglobinopathies, leukemias, or lymphomas)
• Diagnosed immunodeficiency as a result of a pathological condition
• Pharmacologically induced immunodeficiency as a result of prescribed administration of corticosteroids (e.g., any systemic administration of corticosteroids or an inhaled dose equivalent to 800 mg of beclomethasone dipropionate) or chemotherapeutics or as a result of radiation therapy or any other modality capable of altering normal immunologic response
• Known or suspected problem with drug or alcohol abuse
• Investigational drug received within 6 weeks prior to study entry or concurrent participating in a clinical study that includes the administration of an investigational product
• Subjects who 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, spouse/partner, siblings, parents) as well as employees of the investigator.