Safety and Effectiveness of a Seasonal Live Attenuated Influenza Vaccine in a Human Challenge Model of Infection With Wild-type (wt) Influenza A/California/2009 (H1N1)-Like Virus

Inclusion Criteria: * Adult males and non-pregnant females between 18 years and 45 years of age. Children will not be recruited or enrolled in this study for safety considerations and because of the need for isolation. * General good health, without significant medical illness, physical examination findings, or significant laboratory abnormalities as determined by the investigator. * Likely to be susceptible to the challenge virus as determined by a baseline serum HAI antibody titer to the A/California/09 wild-type virus of 1:8 or less. * Agree to storage of blood specimens for future research. * Available for the duration of the trial. * Willingness to participate in the study as evidenced by signing the informed consent document. * Female subjects must agree to use effective birth control methods for the duration of the study (for example, pharmacologic contraceptives including oral, parenteral, and transcutaneous delivery; condoms with spermicide; diaphragm with spermicide; intrauterine device; abstinence from heterosexual intercourse, surgical sterilization). All female subjects will be considered being of child-bearing potential except those who have undergone hysterectomy and those in whom menopause occurred at least 1 year prior to the study. Exclusion Criteria: * Pregnancy as determined by a positive human choriogonadotropin (beta-HCG) test. * Currently breast-feeding. * Evidence of clinically significant neurologic, cardiac, pulmonary, hepatic, rheumatologic, autoimmune, endocrinologic or renal disease by history, physical examination, and/or laboratory studies including urine testing. Levels of alanine aminotransferase (ALT), aspartate transaminase (AST), bilirubin greater than 2 times the upper limit of normal (ULN) or otherwise clinically significant as determined by the Principal Investigator (PI), will be exclusionary at baseline, prior to vaccination. Complete blood count (CBC) with differential outside of the normal reference range and deemed clinically significant by the PI. * Body Mass Index (BMI) of less than 18.5 or greater than 40. * Behavioral or cognitive impairment or psychiatric disease that in the opinion of the investigator affects the ability of the subject to understand and cooperate with the study protocol. * Have medical, occupational, or family problems as a result of alcohol or illicit drug use during the past 12 months. * Other condition that in the opinion of the investigator would jeopardize the safety or rights of a subject participating in the trial or would render the subject unable to comply with the protocol. * History of anaphylaxis. * Allergy to oseltamivir as determined by subject report. * Current diagnosis of asthma or reactive airway disease (within the past 2 years). * History of Guillain-Barré Syndrome. * Known immunodeficiency syndrome. * Use of corticosteroids (excluding topical preparations) or immunosuppressive drugs within 30 days prior to vaccination. * Receipt of a live vaccine within 4 weeks or a killed vaccine within 2 weeks prior to study vaccination. * Receipt of any unlicensed drug within 3 months or 5.5 half-lives (whichever is greater) or any unlicensed vaccine within 6 months of enrollment. * History of a surgical splenectomy. * Receipt of blood or blood-derived products (including immunoglobulin) within 6 months prior to study vaccination. * Current smoker unwilling to stop smoking for the In-patient Challenge Phase of the study. * A current smoker includes anyone stating they currently smoke any amount of a tobacco product. * The decision to exclude a potential subject is determined by medical history and a clinician's clinical judgment based on the physical examination. * After admission to the unit, nicotine patches will be provided to current smokers who request them for the inpatient portion of the study. * Allergy to eggs or egg products. * Household contacts of individuals at higher risk for influenza-related complications, including: Persons greater than or equal to 65 years of age or less than 5 years of age; or persons with chronic pulmonary disease (e.g., asthma, emphysema), chronic cardiovascular disease (e.g., cardiomyopathy, congestive heart failure, ischemic heart disease), metabolic disease (e.g., diabetes mellitus, renal dysfunction, hemoglobinopathies), immunosuppression, neurological and neurodevelopmental conditions, children and teenagers who are receiving long-term aspirin therapy, or women who are pregnant or who are trying to become pregnant. * Positive urine drug toxicology test indicating narcotic use/dependency. * Positive ELISA and confirmatory tests for human immunodeficiency virus-1 (HIV-1), hepatitis C virus (HCV), or hepatitis B (Positive hepatitis B virus surface antigen). * Clinically significant abnormalities on ECG. * Clinically significant abnormality as deemed by the PI on echocardiographic testing. * Known close contact with anyone known to have influenza or influenza-like illness in the past 7 days.