Young Adult Influenza Vaccine Immunogenicity Substudy

Inclusion Criteria: 1. Male or nonpregnant female (as indicated by a negative urine pregnancy test immediately prior to vaccine administration) between the ages of 18 and 40 years, inclusive. 2. 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 (28 days). 3. In good health, as determined by medical history and a targeted physical examination, if necessary. 4. Able to understand and comply with planned study procedures. 5. Able to provide informed consent and be available for all study visits. Exclusion Criteria: 1. Has a known allergy to eggs or other components of the vaccine. 2. Has a positive urine pregnancy test at screening or prior to vaccination (if female), is lactating, or has the intention to become pregnant within 3 months of enrollment in this study. 3. Is undergoing immunosuppression as a result of an underlying illness or treatment. 4. Has an active neoplastic disease or a history of any hematologic malignancy. 5. Is using oral or parenteral steroids, high-dose inhaled steroids (\>800 mcg/day of beclomethasone dipropionate or equivalent) or other immunosuppressive or cytotoxic drugs. 6. Has a history of receiving immunoglobulin or other blood product within the 3 months prior to enrollment in this study. 7. Has received any other licensed vaccines within 2 weeks (for inactivated vaccines) or 4 weeks (for live vaccines) prior to enrollment in this study. 8. 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). 9. Has a history of severe reactions following immunization with contemporary influenza virus vaccines. 10. Has an acute illness, including an oral temperature greater than 100.4 degrees F, within one week of vaccination. 11. Received an experimental vaccine or medication within 1 month prior to enrollment in this study, or expects to receive an experimental vaccine, medication, or blood product during the 4 week study period. 12. Has any condition that would place the volunteer at an unacceptable risk of injury or any condition that in the opinion of the investigator may compromise the safety of the volunteer or integrity of the study.