A total of 88 children between 2 and 9 years of age will be randomized to receive a two dose schedule of either licensed live attenuated trivalent seasonal influenza vaccine (LAIV) or licensed inactivated seasonal influenza vaccine (TIV)or TIV followed by LAIV or LAIV followed by TIV separated by 28 days. Children with a laboratory documented history of prior H1N1 infection will be excluded.

The study will be conducted as a randomized, prospective, open-label evaluation of the clinical tolerability, vaccine virus shedding, and serum and mucosal antibody response to vaccination with either live trivalent influenza vaccine (LAIV) or trivalent influenza vaccine (TIV) in healthy children between the ages of 2 and 9 years. Children will be screened for antibody to A/Brisbane/57/07 (H1N1) and A/California/07/09 (H1N1), A/Perth/16/2009 (H3N2) and B/Brisbane/60/2008 before and at indicated times after the start of the study. They will not be randomized based on antibody levels. Children with prior documented infection with the 2009 pandemic H1N1 virus will be excluded. Vaccine will be administered on days 0 and 28.

Safety of vaccination will be assessed using symptoms collected by parents for 7 days after each dose of vaccine. Serum will be obtained prior to and on day 28 following each dose of vaccine and assessed for antibody by HAI, ELISA, and neutralization techniques. Nasal secretions will be obtained by nasal wick prior to and on day 28 after each dose and assessed for HA-specific IgA (immune globulin A) and IgG (immune globulin G)antibody by ELISA. Nasal swabs will be obtained on days 2, 4, and 7 after each dose of live vaccine and assessed for the presence and magnitude of vaccine virus shedding of the live attenuated vaccine by rtRT-PCR (real-time reverse transcriptase polymerase chain reaction)and TCID50 (50% tissue culture infectious doses)on MDCK(Madin Darby Canine Kidney) cells.

Inclusion Criteria:

• Aged between 2 and 9 years, inclusive.
• No prior history of laboratory documented infection with novel H1N1 virus
• The subject must be in good health, as determined by: vital signs (heart rate <140 bpm; blood pressure: systolic ≥ 90 mm Hg and ≤140 mm Hg; diastolic ≤ 90 mm Hg; oral temperature <100.0ºF (fahrenheit); medical history; and targeted physical examination, when necessary, based on medical history. Stable medical condition is defined as: no recent increase in prescription medication, dose, or frequency of medication in the last 3 months and health outcomes of the specific disease are considered to be within acceptable limits in the last 6 months.
• The subject/parents are able to understand and comply with the planned study procedures, including being available for all study visits.
• The subject/parents have provided informed consent prior to any study procedures. (An assent will be obtained for all children as required by the institutional IRB (Institutional Review Board.)

Exclusion Criteria:

• Subjects with a laboratory documented history of previous novel H1N1 infection.
• History of egg allergy or allergy to other components of vaccine.
• History of wheezing.
• The subject is immunosuppressed as a result of an underlying illness or treatment with immunosuppressive or cytotoxic drugs, or use of anticancer chemotherapy or radiation therapy.
• The subject has an active neoplastic disease.
• The subject has long-term (greater than 2 weeks) use of oral or parenteral steroids, or high-dose inhaled steroids (>800 mg/day of beclomethasone dipropionate or equivalent) within the preceding 6 months (nasal and topical steroids are allowed).
• The subject received immunoglobulin or another blood product within the 3 months prior to enrollment in this study.
• The subject has received an inactivated vaccine within the 2 weeks or a live vaccine within the 4 weeks prior to enrollment in this study or plans to receive another vaccine within the next 28 days (or 56 days for vaccine naïve recipients).
• The subject has an acute or chronic medical condition that, in the opinion of the investigator, would render vaccination unsafe or would interfere with the evaluation of responses. These conditions include chronic conditions recognized as risk factors for influenza complications or as contraindications for live vaccination, including chronic cardiac (exclusive of hypertension) or pulmonary conditions (including asthma), diabetes mellitus, or renal impairment.
• The subject has an acute illness or an oral temperature greater than 99.9 degreesF (37.7 degrees C) within 3 days prior to enrollment or vaccination. Subjects who had an acute illness that was treated symptoms resolved are eligible to enroll as long as treatment is completed and symptoms resolve > 3 days prior to enrollment.
• The subject is currently participating or plans to participate in a study that involves an experimental agent (vaccine, drug, biologic, device, blood product, or medication) or has received an experimental agent within 1 month prior to enrollment in this study, or expects to receive another experimental agent during participation in this study, or intends to donate blood during the study period.
• The subject has any condition that would, in the opinion of the site investigator, place the subject at an unacceptable risk of injury or render the subject unable to meet the requirements of the protocol.
• The subject has a known human immunodeficiency virus, hepatitis B, or hepatitis C infection.
• The subject has a previous history of Guillain-Barré syndrome within 6 weeks of receipt of influenza vaccination.
• The subject has any condition that the principal investigator (PI) believes may interfere with successful completion of the study.

Baseline characteristics were confined to the children enrolled in the second year only. In the second year randomization was confined to the two groups of greatest interest: 1) LAIV IN twice and 2) IIV IM followed by LAIV IN.