FIG. 5.

Long-term protective heterologous immunity in vaccinated mice. Mice (n = 5) were vaccinated and challenged at 1 year postprime with VN/1203, as described in the legend to Fig. 2. (A) Sera collected from vaccinated mice at 11 months postprime (9 months postboost) were subjected to microneutralization assays (39) against the indicated viruses (HK/156, HK/483, VN/1203, and INA/5). A titer of 10 in this assay is negative. (B and C) At 1 year postprime (10 months postboost), vaccinated mice were challenged intranasally with VN/1203 (clade 1). (B) Morbidity was assessed by weight loss and is shown as the average original prechallenge weight. (C) A Kaplan-Meier plot depicts the percent survival of negative-control or H5 HA-vaccinated mice. The control animals shown in panels B and C are the same animals as those in Fig. 2 and are shown here for comparison.