Evaluation of Anti-Hemagglutinin (Anti-HA) Antibodies as Protection From the Flu in Healthy People

-INCLUSION CRITERIA: 1. Greater than or equal to 18 and less than or equal to 50 years of age. 2. Agrees to not use tobacco products during participation in this study. 3. Willingness to remain in isolation for the duration of viral shedding (at a minimum 9 days) and to comply with all study requirements. 4. A female participant is eligible for this study if she is not pregnant or breast feeding and 1 of the following: * Of nonchildbearing potential (i.e., women who have had a hysterectomy or tubal ligation or are postmenopausal, as defined by no menses in greater than or equal to 1 year). * Of childbearing potential but agrees to practice effective contraception or abstinence for 4 weeks prior to and 8 weeks after administration of the influenza challenge virus. Acceptable methods of contraception include 1 or more of the following: 1) male partner who is sterile prior to the female participant s entry into the study and is the sole sexual partner for the female participant; 2) implants of levonorgestrel; 3) injectable progestogen; 4) an intrauterine device with a documented failure rate of \< 1%; 5) oral contraceptives; and 6) double barrier methods including diaphragm or condom with a spermicide. 5. Willing to have samples stored for future research. 6. Prechallenge serum hemagglutination inhibition (HAI) titer against the challenge virus of greater than or equal to 1:40 or less than or equal to 1:10 during a screening visit in protocol #11-I-0183 7. HIV uninfected. EXCLUSION CRITEIRA: 1. Presence of self-reported or medically documented significant medical condition including but not limited to: 1. Chronic pulmonary disease (e.g., asthma, emphysema). 2. Chronic cardiovascular disease (e.g., cardiomyopathy, congestive heart failure, cardiac surgery, ischemic heart disease, known anatomic defects). 3. Chronic medical conditions requiring close medical follow-up or hospitalization during the past 5 years (e.g., diabetes mellitus, renal dysfunction, hemoglobinopathies). 4. Immunosuppression or ongoing malignancy. 5. Neurological and neurodevelopmental conditions (e.g., cerebral palsy, epilepsy, stroke, seizures). 6. Postinfectious or postvaccine neurological sequelae. 2. Have close or household (i.e., share the same apartment or house) high-risk contacts including but not limited to: 1. Persons greater than or equal to 65 years of age. 2. Children less than or equal to 5 years of age. 3. Residents of nursing homes. 4. Persons of any age with significant chronic medical conditions such as: * Chronic pulmonary disease (e.g., asthma). * Chronic cardiovascular disease (e.g., cardiomyopathy, congestive heart failure, cardiac surgery, ischemic heart disease, known anatomic defects). * Contacts who required medical follow-up or hospitalization during the past 5 years because of chronic metabolic disease (e.g., diabetes mellitus, renal dysfunction, hemoglobinopathies). * Immunosuppression or cancer. * Neurological and neurodevelopmental conditions (e.g., cerebral palsy, epilepsy, stroke, seizures). * Individuals who are receiving long-term aspirin therapy. * Women who are pregnant or who are trying to become pregnant. 3. Individual with body mass index (BMI) less than or equal to 18.5 and greater than or equal to 40. 4. Smokes more than 4 cigarettes or other tobacco products on weekly basis. 5. Complete blood count (CBC) with differential outside of the NIH DLM normal reference range and deemed clinically significant by the PI. 6. Chemistries in the acute care, mineral, and/or hepatic panels, and/or any of the following: lactate dehydrogenase, uric acid, creatine kinase, and total protein outside of the NIH DLM normal reference range and deemed clinically significant by the PI. 7. Neutropenia below 1,500 cells/mm(3) (Grade 2 or greater) 8. Urinalysis outside of the NIH DLM normal reference range and deemed clinically significant by the PI. 9. Clinically significant abnormality on electrocardiogram. 10. Clinically significant abnormality as deemed by the PI on echocardiographic testing. 11. Clinically significant abnormality as deemed by the PI on the Pulmonary Function Test (PFT). 12. Recent acute illness within 1 week of admission to the isolation facility. 13. Known allergy to treatments for influenza (including but not limited to oseltamivir, nonsteroidals). 14. Known allergy to 2 or more classes of antibiotics (e.g., penicillins, cephalosporins, fluoroquinolones, or glycopeptides). 15. Receipt of blood or blood products (including immunoglobulins) within 3 months prior to enrollment. 16. Receipt of any unlicensed drug within 3 months or 5.5 half-lives (whichever is greater) prior to enrollment. 17. Receipt of any non-influenza related unlicensed vaccine within 6 months prior to enrollment. 18. Self-reported or known history of current alcoholism or drug abuse, or positive urine/serum test for drugs of abuse (i.e., amphetamines, cocaine, benzodiazepines, opiates, or metabolites, but not tetrahydrocannabinol (THC) or metabolites). 19. Self-reported or known history of psychiatric or psychological issues deemed by the PI to be a contraindication to protocol participation 20. Known close contact with anyone known to have influenza in the past 7 days. 21. Any condition or event that, in the judgment of the PI, is a contraindication to protocol participation or impairs the volunteer s ability to give informed consent.