The invention provides antibody reagents for screening for seed viruses, in particular, antibodies that bind to one or more discontinuous epitopes in hemagglutinin (HA) polypeptide of human influenza virus (H1N1 strain). Additionally, the invention relates to compositions, kits, supports, and biologicals comprising the antibodies or fragments thereof. Also provided are nucleic acids encoding such antibodies or fragments, including, cells and/or hybridomas which generate such molecules. Additional embodiments relate to the immunogens useful in generating the antibodies, including nucleic acids encoding such immunogens, and compositions comprising such immunogens. Further embodiments relate to methods for screening for seed viruses, including human influenza type A virus seed viruses, using the antibodies or fragments thereof. Embodiments of the invention also provide for the prevention, reduction of incidence of, or therapy of subjects having influenza, via administration of the seed viruses, or vaccines and/or pharmaceutical compositions containing the seed viruses.