Serum IAV-specific antibody levels in pigs vaccinated with H1N1pdm09 whole inactivated virus vaccine (WIV) or commercial quadrivalent vaccine (COM) in the presence of IAV-specific maternally-derived antibodies (MDA). Pigs were vaccinated at 16 weeks of age, when MDA HI titers dropped below the limit of detection (dotted line). (A) Reciprocal geometric mean HI titers against H1N1pdm09 antigen and mean optical density (O.D.) in influenza A virus nucleoprotein (NP)-specific ELISA at 1, 9, 13 and 16 weeks of age; reciprocal geometric mean HI titers at 0, 14 and 28 days post vaccination against H1N1pdm09 (B), H3N2-IV (C), γ-H1N1 (D), and δ2-H1N1 (E) antigens. Asterisks indicate significant difference between MDA-statuses within the same vaccine (P ≤ 0.05).