The purpose of this study is to develop a nasal model for influenza infection using the live attenuated influenza vaccine (LAIV). The investigators will administer LAIV to healthy adult volunteers in order to simulate influenza infection, and obtain nasal specimens to measure influenza virus and inflammatory/immune responses. In a subset of participants, cystic fibrosis transmembrane conductance regulator (CFTR) function will also be evaluated via measurement of nasal potential difference (NPD)

Inclusion Criteria:

• ages 18-49 years old,
• not yet received influenza vaccine for 2019-2020, and
• capable of giving signed informed consent.

Exclusion Criteria:

• Immunocompromising condition (e.g. HIV/AIDS, chemotherapy, immune suppressing medications),
• active smoking within past 6 months,
• asthma, chronic lung/liver/kidney /neurologic/hematologic/metabolic disorders,cardiovascular disease (excluding isolated hypertension), diabetes mellitus, disease, congestive heart failure,
• pregnancy,
• current or recent (within the past month) upper/lower respiratory tract infection, chronic sinusitis/nasal allergies requiring frequent or daily therapy (including topical corticosteroids),
• prior adverse reaction to influenza vaccine,
• history of Guillain-Barre syndrome,
• egg allergy,
• close contact with an individual with severe immunodeficiency/immunosuppression.