ARDS CD4 T cell Influenza A virus (IAV) Influenza vaccine Influenza virus T cell adaptive immunity antibodies broad neutralizing antibody(bnAb) epitopes germinal centers hemagglutin stalk hemagglutinin hemagglutinin (HA) of influenza virus heterosubtypic immunity of influenza humoral response immune response immunogenicity imprinting infection influenza influenza A virus influenza vaccine influenza virus innate immunity live attenuated influenza vaccine lung mPLEX-Flu assay master donor virus memory