Fig. 1.

HA-specific antibody responses following DNA vaccination and challenge. Pigs were vaccinated twice (arrows) i.d. with needle-free delivery with 800 μg (n = 5) or 500 μg (n = 5), or not DNA vaccinated at all (n = 5). Levels of IgG in the pre- and post-challenge sera were measured by ELISA against recombinant HA (H1N1pdm09) (A). Hemagglutination inhibition antibody responses in the pre- and post-challenge sera against H1N1pdm09 were measured (B). A Hi-titer cut-off of 20 IE/ml is indicated. Error bars indicate the mean ± SEM, and significant differences from the no-vaccine control group are indicated by **: p < 0.01; *: p < 0.05.