Serum responses after experimental vaccination. The serum response on days 0, 7, and 28 after a single vaccination was measured using an ELISA with calibrated standard antisera. Data are shown for HD (red bars), dose groups DL1/2 (blue bars), and DL3/4 (green bars) as box plots. ns, not significant; ∗P < .05; ∗∗P < .01; ∗∗∗P < .001. Dotted lines indicate the protective titer of individual vaccine antigens.