The invention relates to a method for isolating a polypeptide reactive to influenza A hemagglutinin, comprising the steps of preparing a library of nucleic acid sequences, wherein each member of said library is attached to a polypeptide sequence encoded thereby, selecting members of said library by contacting the members with a panning antigen, wherein the panning antigen comprises a hemagglutinin stem region polypeptide sequence, subsequently removing members unreactive to the panning antigen, and selecting a member of said library by determining its binding to at least 5 influenza A hemagglutinin subtypes of subtype group 1 and 2. The invention further relates to polypeptides, particularly antibodies, obtainable by this method, that neutralize at least five influenza A subtypes of subtype group 1 and 2, to vaccines and uses thereof.
