Inclusion Criteria:

• Medically stable adults, aged 18-49 years.
• Provided informed consent prior to any study procedures.
• Able to comply with all study procedures.
• Available for follow-up for the duration of the influenza season.
• Women of child-bearing potential had a negative urine pregnancy test at the time of randomization and were willing to use an adequate form of contraception during the course of the study.

Exclusion Criteria:

• Any history of immunodeficiency or treatment with immunosuppressive medications. (Use of inhaled steroids or of topical steroids was not considered immunosuppressive; receipt of systemic glucocorticosteroids was not allowed if daily intake was >10 mg of prednisone or equivalent).
• Presence of high-risk conditions or other characteristics considered to be indications for influenza vaccination, as defined by the Advisory Committee on Immunization Practices (ACIP).
• Acute febrile illness (defined as having a temperature ≥100degreesF) or upper respiratory tract illness within 72 hours of vaccination.
• Use of experimental vaccines or any influenza vaccine after May 31st 2004 for the 2005 Southern Hemisphere or 2004 to 2005 Northern hemisphere epidemic seasons.
• Use of any experimental medication within 30 days prior to study vaccination
• Women who were pregnant or breast-feeding.
• Subjects with a history of Guillain-Barré syndrome.
• Receipt of parenteral immunoglobulin within 30 days prior to study vaccination.
• Any acute or chronic condition that, in the opinion of the investigator, would render vaccination unsafe or interfere with the evaluation of response.