Human IgA antibodies after 2014/2015 inactivated influenza virus vaccination primarily bind to H1 HA. (A) Eight human donors were vaccinated with the recommended dose of the 2014/2015 QIV. Seven days after vaccination, plasmablasts were isolated from peripheral blood, and sequencing was performed to specifically isolate IgA variable regions from single-cell suspensions. Cloning of IgA variable regions into an IgG1 backbone was performed prior to expression and purification of mAbs. ELISAs were performed using recombinant HA proteins: (B) A/California/04/2009 H1, (C) A/Victoria/361/2011 H3, (D) B/Massachusetts/2/2012 BHA, and (E) B/Malaysia/2506/2004 BHA. AUC values are reported as a representation of each binding curve. (F) The number of mAbs which bound to each antigen tested by ELISA is reported for the entire antibody panel. Negative control is assay run without antibody present.