Inclusion Criteria:

• Previous recipient of inactivated Influenza A/H5N1 vaccine in study DMID 04-063.
• Male or nonpregnant female (as indicated by a negative urine pregnancy test immediately prior to vaccine administration) between the ages of 18 and 65 years, inclusive.
• Women of childbearing potential who are at risk of becoming pregnant must agree to practice adequate contraception (i.e., barrier method, abstinence, and licensed hormonal methods) for the entire study period.
• Is in good health, as determined by vital signs (heart rate, blood pressure, oral temperature), medical history and a targeted physical examination based on medical history.
• Able to understand and comply with planned study procedures.
• Provides informed consent prior to any study procedures and is available for all study visits.

In order to be eligible to participate in the blood specimen collection substudy, subjects must also meet the following additional inclusion criteria:

• Previously achieved a 4-fold or greater increase from baseline in GMT following the second immunization with A/H5N1 approximately 28 days after dose 2 of study DMID 04-063 (approximately Day 56).
• Agrees to the storage of clinical specimens for an indefinite period of time at a central laboratory for use in future research.

Exclusion Criteria:

• Received placebo in DMID Study 04-063.
• Known allergy to eggs or other components of the vaccine or latex.
• Has a positive urine pregnancy test prior to vaccination (if female of childbearing potential) or women who are breastfeeding.
• Is undergoing immunosuppression as a result of an underlying illness or treatment.
• Has or had a neoplastic disease diagnosed or treated within the last 5 years or any lifetime history of hematologic malignancy. Those participants with any history of benign basal cell carcinoma of the skin may participate.
• Is using oral or parenteral steroids, high-dose inhaled steroids (>800 micrograms/day of beclomethasone dipropionate or equivalent) or other immunosuppressive or cytotoxic drugs.
• Has a history of receiving immunoglobulin or other blood product within the 3 months prior to enrollment in this study.
• Has received any other licensed vaccines within 2 weeks (for inactivated vaccines) or 4 weeks (for live vaccines) prior to enrollment in this study.
• Has an acute or chronic medical condition that, in the opinion of the investigator, would render vaccination unsafe or would interfere with the evaluation of responses (this includes, but is not limited to: known chronic liver disease, significant renal disease, unstable or progressive neurological disorders, diabetes mellitus, and transplant recipients).
• Has a history of severe reactions following immunization with contemporary influenza virus vaccines.
• Has an acute illness, including an isolated oral temperature greater than 100.4 degrees F, within 1 week of vaccination.
• Received an experimental agent (vaccine, drug, biologic, device, blood product, or medication) within 1 month prior to enrollment in this study other than DMID 04-063, or expects to receive an experimental agent during the 7-month study period.
• Has a history of alcohol abuse or drug abuse (including chronic pain medication) in the last 5 years.
• Has any condition that would, in the opinion of the site investigator, place the subject at an unacceptable risk of injury or render the subject unable to meet the requirements of the protocol.