Figure 1.

Evolution of hemagglutination inhibition (HI) antibody titers against the strains used for infection, (A) NC95, and vaccination, (B) G08 and (C) PA10. The titers were determined at weeks 0, 4, 7, 11, and 15 following infection with NC95. The interval between infection (Inf.) and the first vaccination (1°) was 7 weeks. The second vaccination (2°) was administered 4 weeks later. The different groups are shown on the x-axis. The dotted lines indicate the detection limit, which in this case was a titer of 10. Asterisks denote statistical differences between groups that received heterologous (NC95-PA10-G08) and homologous (NC95-G08-G08) vaccines in Mann–Whitney U test (p < 0.05).