Patient description: A 42-year-old healthy woman came to the clinic to have her flu shot in early October. She works in a rehab center and has no underlying disease. It's her first time getting the vaccine this year. She is married for 5 years and uses barrier methods of contraception. Her menstrual cycle is irregular. She does not smoke. She is not on any medications. She exercises regularly for 30 minutes a day at least 5 days a week. She has no history of allergies to any food or drugs. Her past surgical history is significant for tonsillectomy and she is otherwise healthy.

Clinical trial eligibility criteria: eligible ages (years): 19.0-49.0,  Influenza, Human Males and females in good general health, 19 to 49 years of age. 2. Subjects must provide written informed consent. 3. Subjects must be willing to participate through study completion. 4. Have not been vaccinated for influenza virus in the current season or had a known influenza virus infection in the current season 5. Subjects must be willing to undergo nasal washes and provide parotid saliva, urine and blood samples per protocol for safety and immunogenicity analyses. 6. Females of childbearing potential must have a negative urine pregnancy test. 7. A female volunteer must Agree to consistently use effective contraception from at least 21 days prior to enrollment through the Day 84 clinic visit for sexual activity that could lead to pregnancy Effective contraception is defined as using any of the following methods condoms (male or female) with or without spermicide diaphragm or cervical cap with spermicide intrauterine device (IUD) hormonal contraception, or successful vasectomy in the male partner (considered successful if a volunteer reports that a male partner has [1] documentation of azoospermia by microscopy or [2] a vasectomy more than 2 years ago with no resultant pregnancy despite sexual activity post-vasectomy) Or not be of reproductive potential, such as having reached menopause (no menses for 1 year) or having undergone hysterectomy, bilateral oophorectomy, or tubal ligation Or be sexually abstinent  Pregnant or lactating women. 2. Any flu/cold, or respiratory tract symptoms and/or fever greater than 101 ºF in the 3 days prior to study enrollment and/or initial vaccination. 3. Any intranasal medication administered in the 10 days prior to study enrollment and/or initial vaccination. 4. History of Bell's palsy, significant cardiac history including history of arrhythmias, coagulopathy, history of cardiovascular accident, bone marrow diseases, known or suspected, autoimmune diseases (such as but not limited to psoriasis, rheumatoid arthritis, hyperthyroidism, hypothyroidism, vasculitis, Raynaud's phenomenon, rhabdomyolysis and myositis, nephritis, systemic lupus erythematosus and sarcoidosis, hemolytic anemia) and any history of malignancy. 5. History of chronic rhinitis or presence of pre-existing nasal septal defect, nasal polyps or other gross abnormalities that might impact vaccine administration, or any previous nasal cautery or significant surgery for nasal septal defects. 6. Any regular past or current use of intranasal illicit drugs, or a history of intravenous illicit drug use. 7. Asthma, or other chronic respiratory disorders, of any severity, even if mild. 8. Reactive HBVsAg or reactive HCV Ab. 9. HIV positive by history or by screening test. 10. History of alcohol or other substance abuse, or history of depression or suicidal ideation, or a suicide attempt within two (2) years of screening. A score of 5 or greater on the PHQ-9 at Baseline indicates symptoms of depression and will subject. A score of greater than zero on question nine (9) of the PHQ-9 at Baseline indicates suicidal ideation and will subject. 11. Immunosuppressed, altered or compromised immune status as a consequence of disease (i.e. asplenia, recurrent severe infections) or chronic treatment (more than 14 days) with systemic corticosteroids (including inhaled or intranasally-administered drugs), alkylating drugs, anti-metabolites, radiation, or other immunosuppressive therapies within the preceding 6 months. 12. Administration of immunoglobulins and/or any blood products within 3 months prior to enrollment. 13. Receipt of an influenza vaccine within the past 6 months. 14. Receipt of any vaccine in the past 30 days. 15. Receipt of any investigational drug in the past 30 days. 16. Known diabetes mellitus. 17. History of anaphylaxis, Guillain-Barré Syndrome, or angioedema. 18. Blood pressure > 140/90 (either or both values) at screening or enrollment. 19. Any medical, psychiatric, or social condition, or occupational or other responsibility that, in the judgment of the investigator, would interfere with, or serve as a contraindication to, protocol adherence, assessment of safety or reactogenicity, or a participant's ability to give informed consent. 20. History of taking antiviral drugs active against influenza A and/or B in last 72 hours before FluMist® administration. 21. Hypersensitivity to eggs, egg proteins, gentamicin, gelatin, or arginine, or life threatening reactions to previous influenza vaccinations. 22. Clinically significant abnormality on screening EKG