XK and influenza: The HA glycoprotein is the primary influenza vaccine target that stimulates higher levels of HA inhibition (HI) and neutralizing antibodies (NAB) titers, stronger cellular immune responses, and confers better protection against homologous or heterologous H5N1 virus challenge than NA, nucleoprotein (NP), matrix protein 1 (M1) or M2 based vaccines [142,143,144,145].