Figure 3.

Neutralizing antibody titers determined using 2 cell line–based neutralization assays. Sera from day 0 and day 182 were serially diluted to generate a 50% inhibitory dilution (ID₅₀) against H9-adapted MN in the H9 assay (A) and A3R5-adapted US1 in the A3R5 assay (B). Neutralization in the postimmunization sera (day 182) was determined using the preimmunization sera (day 0) as baseline. Group means are shown; groups with titers significantly higher than the placebo control are marked with an asterisk. The dotted lines represent the negative cutoffs.