The objective of the protocol is to investigate the human innate and adaptive immune responses in blood (only for adults) and nasopharyngeal mucosa resident cells to the live, attenuated influenza vaccine (LAIV) in both adults and children. The investigators hope to learn how the upper respiratory tract (URT) epithelial cells, the primary target of respiratory viruses, and the B cells and T cells, two major components of the immune system, respond to the influenza vaccine.~The volunteers will be enrolled in two age groups:~Group A: Up to 12 healthy non-twin volunteers, 2-8 years old, will be given seasonal LAIV. Each volunteer will complete a total of 3 visits. Volunteers will be divided in 2 sub-groups A-1 (n=6) and A-2 (n= 6) in order to collect nasopharyngeal swabs on different schedules (Day 1 or Day 2). Volunteers will be assigned to these sub-groups based on convenience sampling. Both sub-groups will complete the Day 0 and Day 28 visits and one visit at either Day 1 or Day 2 post-immunization. Specimens will include nasopharyngeal swabs collected at Day 1 for Sub-group A1 and Day 2 for Sub-group A-2, and Day 28 for both sub-groups. No blood samples will be collected in this age group.~Children with no prior influenza vaccine history will receive a second dose of vaccine (LAIV) at least 28 days after the first study dose, according to the ACIP guidelines.~Group B: Up to 18 healthy non-twin volunteers, 18-49 yrs old, will be given seasonal LAIV vaccine. Each volunteer will complete a total of 5 visits. Volunteers will be divided into 3 sub-groups B-1, B-2 and B-3 in order to collect nasopharyngeal swabs and blood specimens on different schedules (Day 0-6 hrs, Day 1 or Day 2). Volunteers will be assigned to these sub-groups based on convenience sampling. All sub-groups will complete visits at Day -7, Day 0 pre-immunization, Day 7 and Day 28 and 1 additional time point: Sub-group B-1 at Day 0, 6 hours post-immunization, Sub-group B-2 at Day 1 and Sub-group B-3 at Day 2. A nasopharyngeal swab will be collected at each visit except for Day 0 (baseline) and Day 7. A blood sample will be collected at each visit except Day -7
The purpose of the study is to investigate and compare the human immune response in epithelial cells of the nasopharyngeal mucosa and in blood to live, attenuated influenza vaccine (LAIV) in adults and in children.