Evaluating the Safety and Immunogenicity of a Live Attenuated Virus Vaccine to Prevent Influenza H3N2v Disease

Inclusion Criteria: * Males and non-pregnant females between 6 and 26 years of age inclusive. * For children, presence of an adult caregiver who is in good health and able to understand and carry out the requirements * General good health, without significant medical illness, physical examination findings, or significant laboratory abnormalities as determined by the investigator. * Agree to storage of blood specimens for future research. * Available for the duration of the trial. * Willingness to participate in the study as evidenced by signing the informed consent document. Verbal assent will be obtained from minors 6 to 12 years of age and signed assent will be obtained from minors 13 and older. * Female subjects of childbearing potential must agree to use effective birth control methods for the duration of the study (e.g., pharmacologic contraceptives including oral, parenteral, and transcutaneous delivery; condoms with spermicide; diaphragm with spermicide; intrauterine device; abstinence from heterosexual intercourse, surgical sterilization). Exclusion Criteria: * Anticipated direct routine \[e.g. weekly or more frequent\] contact with individuals younger than the designated age groups being studied as a result of household contact, occupation, or participation in day care with such individuals. * Pregnancy as determined by a positive urine or serum human choriogonadotropin (β-HCG) test. * Currently breast-feeding. * Evidence of clinically significant neurologic, cardiac, pulmonary, hepatic, rheumatologic, autoimmune, or renal disease by history or physical examination. * 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. * Other condition that, in the opinion of the investigator, would jeopardize the safety or rights of a subject participating in the trial or would render the subject unable to comply with the protocol. * History of anaphylaxis. * Allergy to oseltamivir as determined by subject report. * Current diagnosis of asthma or reactive airway disease (within the past 2 years). * Use of aspirin or salicylate-containing medications within 28 days prior to randomization or expected receipt through 28 days after final vaccination. * History of Guillain-Barré Syndrome. * Known history of HIV, hepatitis C, or active hepatitis B infection. * Known immunodeficiency syndrome. * Use of corticosteroids (excluding topical preparations) or immunosuppressive drugs within 30 days prior to vaccination. * Receipt of a live vaccine within 4 weeks or a killed vaccine within 2 weeks prior to study vaccination. * Receipt of blood or blood-derived products (including immunoglobulin) within 6 months prior to study vaccination. * Travel to the Southern Hemisphere within 14 days prior to study vaccination. * Travel on a cruise ship within 14 days prior to study vaccination. * Receipt of another investigational vaccine or drug within 30 days prior to study vaccination. * Allergy to eggs or egg products, gentamicin, or gelatin. * Chronic use of intranasal medications.