The PBMCs were isolated from whole blood, washed, counted, and banked in freezing medium (heat-inactivated fetal bovine serum with 10% dimethyl sulfoxide) in liquid nitrogen until isolation of RNA was performed using a RNeasy Minikit (QIAGEN). Laboratory staff conducting the HAI and MN assays were blinded to vaccine assignment. Peripheral blood mononuclear cell RNA was assessed for integrity and concentration using an Agilent Tape Station and Qubit Fluorometric Quantification.