The primary objective of this study was to determine the immunologic noninferiority of MEDI8662, a quadrivalent live attenuated influenza vaccine (Q/LAIV) (delivered intranasally using the blow-fill-seal [BFS] delivery system) (Q/LAIV-BFS) to two trivalent formulations of licensed FluMist (delivered intranasally using the Becton Dickinson [BD] Accuspray™ device) by comparing the strain-specific geometric mean titers (GMTs) post dosing.