Antibody responses to influenza a H1N1 vaccine compared to the circulating strain in influenza vaccine recipients during the 2013/2014 season in North America

2013/2014 IIV3 and LAIV4 recipients had consistently lower MN antibody titers against H1N1-14 compared with H1N1-09. The HA K166Q mutation, located in a neutralizing epitope, probably contributed to these findings.