Kinetics of B-Cell Responses to Live, Attenuated Influenza Vaccine (LAIV) in Young Children Two Years of Age

Inclusion Criteria 1. Otherwise healthy children, aged 24-35 months of age, inclusive. 2. Parent(s) or guardian(s) willing to sign informed consent. 3. Availability for follow-up for the planned duration of the study. 4. Acceptable medical history by screening evaluation and brief clinical assessment. 5. Able to understand and comply with planned study procedures Exclusion Criteria 1. Prior vaccination with LAIV. 2. TIV vaccination during two prior influenza vaccine seasons 3. Known prior MD diagnosis of, or hospitalization for influenza 4. History of asthma, active/recurrent wheezing or reactive airways disease 5. History of immunodeficiency 6. Known or suspected impairment of immunologic function including, but not limited to, clinically significant liver disease; diabetes mellitus; moderate to severe kidney impairment. 7. Known underlying medical conditions (e.g. hemoglobinopathy, congestive heart failure) predisposing to influenza complications. 8. Household contact with immunodeficiency due to disease, medication or radiation 9. Child receiving aspirin therapy or aspirin-containing therapy 10. History of Guillain-Barré syndrome 11. Malignancy, other than squamous cell or basal cell skin cancer 12. Autoimmune disease 13. Use of immunosuppressive medication. Corticosteroid nasal sprays are permissible. 14. Use of antiviral agents against Influenza A and/or B (such as Tamiflu, Relenza, Flumodine, Symmetrel) less than 48 hours before and/or less than two weeks after administration of FluMist. 15. History of blood dyscrasias, renal disease, or hemoglobinopathies requiring regular medical follow-up or hospitalization during the preceding year. 16. Use of investigational agents within 30 days prior to study 17. Receipt of blood products or immunoglobulin in the past 6 months 18. Donation of the equivalent of a unit of blood within 6 weeks prior to enrollment 19. Acute febrile illness on the day of vaccination 20. Known allergies to any component of the vaccine, including eggs or egg products, gentamicin, gelatin,or arginine, or known life-threatening reactions to previous influenza vaccinations. 21. Concurrent participation in other investigational protocols or receipt of an investigational product within the previous 30 days or planned receipt of an investigational product within 28 days following the last immunization dose. 22. Any condition that, in the opinion of the investigator, might interfere with study objectives