Clinical Efficacy of Trivalent Live-Attenuated Influenza Vaccine (LAIV) Among Children in Senegal

Inclusion Criteria: * Healthy male or female child at least 24 months of age and no older than 71 months of age at the time of study vaccination. * A child whose parent or guardian's primary residence, at the time of study vaccinations, is within the Niakhar DSS and who intends to be present in the area for the duration of the trial. * A child whose parent or legal guardian is willing to provide written informed consent prior to the participant's study vaccination Exclusion Criteria: * Serious, active, medical condition, including: chronic disease of any body system,chronic infections such as tuberculosis, genetic disorders, such as Down's syndrome or other cytogenetic disorder, known or suspected disease of the immune system of any kind. * History of documented hypersensitivity to eggs or other components of the vaccine (including gelatin, sorbitol, lactalbumin and chicken protein), or with life-threatening reactions to previous influenza vaccinations. * History of Guillain-Barré syndrome. * Receipt of immunosuppressive agents, including systemic corticosteroids, during the month before planned study vaccination. * Receipt of aspirin therapy or aspirin-containing therapy within the two weeks before planned study vaccination. * History of any severe allergic reaction with generalized urticarial, angioedema, or anaphylaxis. * Receipt of an influenza vaccine within the past 12 months. * Has any condition determined by investigator as likely to interfere with evaluation of the vaccine or be a significant potential health risk to the child or make it unlikely that the child would complete the study. Temporary Contraindications: * Acute illness accompanied by a body temperature of 37.5°C or above (axillary measurement) within 14 days of enrollment visit. * Any acute respiratory infection within 14 days of enrollment visit. * Any illness accompanied by active wheezing within 14 days of enrollment visit.