Serological characterization of pre-pandemic IVIG (open bars) and post-pandemic H-IVIG (hatched bars). Antibody titers against the seasonal H1N1 strain A/New Caledonia/20/1999 (sH1N1) (white bars) and pandemic A/California/07/2009 (pH1N1) (grey bars) were determined by hemagglutination inhibition (HI), microneutralization (MN) and enzyme-linked lectin assay (ELLA, reported as NA inhibition [NAi]), respectively. Results are given as geometric mean titer (GMT) ± 95% confidence interval (CI). Statistical differences were calculated by unpaired Student t-test analysis (GraphPad Prism software). *** P < 0.0001. GMTs were calculated by testing 13 individual lots of IVIG and 2 lots of H-IVIG.