The purpose of this study is to demonstrate the efficacy of an investigational Vero cell-derived, trivalent, seasonal influenza vaccine to prevent infection with an influenza virus that is antigenically similar to one of the three strains in the vaccine. Subjects will be randomized in a double-blind fashion to receive a single intramuscular injection of either the investigational vaccine or placebo. Blood will be drawn from all subjects for a determination of hemagglutination inhibition antibody titers on Days 0 and 21, body temperature and injection site reactions will be monitored daily for 7 days. In addition, subjects must return to the clinic promptly to have swab samples of their nose and throat taken whenever they feel flu symptoms and all subjects will be monitored for adverse events until Day 180.

Inclusion Criteria:

• Subject has an understanding of the study
• Subject agrees to study provisions
• Subject gives written informed consent prior to study entry
• Subject is accessible by telephone or electronic mail to receive reminders from the study site
• If female and capable of bearing children, subject has a negative urine pregnancy test result within 24 hours of the vaccination on Study Day 0 and agrees to employ adequate birth control measures through the first 60 post-vaccination days.

Exclusion Criteria:

• Subject has any of the risk factors for complications from influenza infection as defined by the Centers for Disease Control and Prevention (CDC, 2008a):

  • 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 and thyroid disorders)
  • Immunosuppression (including immunosuppression caused by medications, congenital etiologies 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 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

• Subject is unable to lead an independent life as a result of either physical or mental handicap

• Subject has a history of severe allergic reactions or anaphylaxis (e.g., urticaria or asthma that is clinically severe)

• Subject has an oral temperature of >= 99.5° F (37.5°C) on the day of vaccination in this study. [NOTE: A subject meeting this exclusion criterion may be rescheduled for vaccination and study entry at a later date provided that certain requirements [in the study protocol] are met)

• Subject has a rash or dermatologic condition or tattoos which may interfere with injection site reaction rating

• Subject has received a blood transfusion, blood products or immunoglobulins within 90 days of study entry

• Subject has received a live vaccine within 4 weeks or inactivated or subunit vaccine within 2 weeks of study entry

• Subject has previously been vaccinated against influenza for the 2008/2009 northern hemisphere influenza season

• Subject has a functional or surgical asplenia

• Subject has a known or suspected problem with alcohol or drug abuse;

• Subject was 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

• Subject is 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](streamdown:incomplete-link)