The purpose of this study is to compare two licensed influenza vaccines (Fluzone and Fluarix) in terms of the immune response elicited and the safety/ any symptoms that may occur for up to six months after vaccination.

• Experimental design: multi-center, randomized (1:1), observer-blind, active-controlled study in 2 parallel groups with approximately:
• Study vaccine: full dose of Fluarix by IM administration.
• Control vaccine: full dose of Fluzone by IM administration.
• Two scheduled visits per subject at days 0 (visit 1) and 21(visit 2) with blood sample collected at each visit to evaluate the immune response. There will be a final contact with each subject 6 months after vaccination for safety follow up and study conclusion.
• Vaccination schedule: one IM injection at day 0.
• Type of study: Self contained.

Inclusion Criteria:

• All adults 18 years and older.
• Subjects who the investigator believes can and will comply with the requirements of the protocol (e.g., return for follow-up visit and completion of the diary cards) should be enrolled in the study.
• Written informed consent obtained from the subject.
• If the subject is female, she must be of non-childbearing potential, i.e. either surgically sterilized or one year post-menopausal; or, if of childbearing potential, she must be abstinent or have used adequate contraceptive precautions .

Exclusion Criteria:

• Use of any investigational or non-registered product (drug or vaccine) within 30 days preceding the administration of the study vaccine, or planned use during the study period.
• Has received any other licensed vaccines within 2 weeks (for inactivated vaccines) or 4 weeks (for live vaccines) prior to enrollment in this study.
• History of hypersensitivity to a previous dose of influenza vaccine.
• History of allergy or reactions likely to be exacerbated by any component of the vaccine(s) including egg, chicken protein, gelatine, formaldehyde, gentamicin sulphate, thimerosal or sodium deoxycholate.
• Acute disease at the time of enrollment. (Acute disease is defined as the presence of a moderate or severe illness with or without fever. All vaccines can be administered to persons with a minor illness such as diarrhea, mild upper respiratory infection with or without low-grade febrile illness, i.e. Oral temperature <37.5°C (99.5°F) / Axillary temperature <37.5°C (99.5°F)).
• History of Guillain Barré syndrome within 6 weeks of prior receipt of inactivated influenza virus vaccine.
• Pregnancy and lactating females.

Patient-level data for this study will be made available through www.clinicalstudydatarequest.com following the timelines and process described on this site.