The primary purpose of this study is to demonstrate the efficacy of an investigational Vero-cell derived influenza vaccine to prevent infection in an adult population with an influenza virus that is antigenically similar to one of the three strains in the vaccine. All subjects will be randomized to receive a single 0.5 ml intramuscular injection from one of three lots of seasonal Vero-cell derived influenza vaccine or saline placebo. Subjects will be monitored for 180 days following vaccination for occurrence of adverse events. For determining antibody response, subjects will have one blood draw before and one blood draw 21 days after vaccination.

Inclusion Criteria:

Male and female subjects who

• are 18 to 49 years of age, inclusive, on the day of screening
• have an understanding of the study, agree to its provisions 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 of the vaccination on Study Day 0 and agree to employ adequate birth control measures. For the purposes of this study adequate birth control measures incorporate two types of the following FDA approved birth control measures through 60 days after the vaccination: hormonal types of birth control (such as implants, birth control pills, patches or other methods) or an intrauterine device, OR an additional barrier type of birth control measure (i.e., condoms, diaphragms, cervical caps, etc.).

Exclusion Criteria:

Subjects who have any of the risk factors for complications from influenza infection as defined by the Centers for Disease Control and Prevention (CDC):

• pregnancy
• chronic disorders of the pulmonary or cardiovascular system including asthma (hypertension is not considered a high risk condition)
• chronic renal disorders
• chronic hepatic disorders
• chronic hematological disorders
• chronic metabolic disorder (including diabetes mellitus)
• immunosuppression (including immunosuppression caused by medications or HIV)
• any condition that can compromise respiratory function or the handling of respiratory secretions or that can increase risk for aspiration (e.g., cognitive dysfunction, spinal cord injuries, seizure disorders or other neuromuscular disorders)
• residence in a nursing home or other chronic care facility that houses persons of any age who have chronic medical conditions
• household contact with children aged 0 to 59 months or of someone who is included in the risk categories listed above
• employment as a health care worker

Subjects are also excluded if they

• are unable to lead an independent life as a result of either physical or mental handicap
• have a history of severe allergic reactions or anaphylaxis
• have an 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 provided: 1.) oral temperature has decreased to < 99.5°F (37.5°C) on rescheduled date, 2.) all other inclusion/exclusion criteria are met, 3.) the rescheduled date is no more than 14 days past the initial screening date, 4.) the study site is still enrolling subjects]
• have a rash or dermatologic condition or tattoos which may interfere with injection site reaction rating
• have received a blood transfusion or immunoglobulins within 90 days of study entry
• have received a live vaccine within 4 weeks or inactivated vaccine within 2 weeks of study entry
• have previously been vaccinated against influenza for the 2007/2008 northern hemisphere influenza season
• have 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, spouse/partner, siblings, parents) as well as employees of the investigator.