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): 18.0-49.0,  Normal Physiology Adult males and females between 18 and 49 years of age Females of child-bearing potential must have a negative serum beta-human choriogonadotropin (HCG) on Day -7 and agree to use an effective birth control method 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 General good health, without significant medical illness, physical examination findings, or significant laboratory abnormalities as determined by the investigator Agree to storage of blood, NP swab, and RNA specimens for future research Available for the duration of the study. Subjects must be willing and able to make follow-up visits as specified by the protocol  Any contraindiciations for adults for the receipt of LAIV: --Hypersensitivity to eggs, egg proteins, gentamicin, gelatin, or arginine,or life-threatening reactions to previous influenza vaccination Currently breast-feeding Evidence of clinically significant neurologic, cardiac, pulmonary, hepatic, rheumatologic, autoimmune, or renal disease by history, physical examination, and/or laboratory studies including urine testing. Clinically significant alanine aminotransferase (ALT) levels, as determined by one of the protocol investigators will be exclusionary at baseline, prior to vaccination Evidence of upper respiratory tract illness (URI) including fever, sore throat, and rhinorrhea. Enrollment of subjects with evidence of URI on Study Day -7 will be temporarily deferred Deviated nasal septum or nasal obstruction Body Mass Index greater than 35 NIH employee involved in direct patient care, consistent with the NIH CC policy that employees should avoid patient care for 5 days following receipt of LAIV. In addition, NIH employees must not be under the supervision of the study principal or associate investigators 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 Seropositive to the influenza A component viruses of seasonal LAIV (serum HAI titer of greater than or equal to 1:10) Has had medical, occupational, or family problems as a result of alcohol or illicit drug use during the past 12 months