FIG 2.

VSV-H1 and VSV-cH9/1 vaccination and H5N1 challenge experiment. (A) Schematic of the prime-boost-challenge vaccination experiments: i.m. and i.n. vaccinations, H5N1 heterologous influenza challenge. Intranasal vaccinations were performed with 2 × 10⁵ PFU, and i.m. vaccinations were performed with 4.5 × 10⁵ PFU. (B) Serum reciprocal endpoint ELISA titers of mice vaccinated with VSV-H1 (prime) and VSV-cH9/1 (boost). Intramuscular vaccination results in greater boost, but overall serum antibody titers postboost are greater for i.n.-vaccinated animals. (C) Vaccinated mice were challenged i.n. 1 month postboost with 10 LD₅₀ of heterosubtypic H5N1 (HALo) influenza virus. Weights were recorded daily for 14 days postchallenge and are graphically displayed as the mean percentage of the prevaccination weight. Error bars represent the 95% CI of the mean weight. All control mice died or required euthanasia per protocol by day 8 postchallenge. Significant differences between groups are indicated in the graph. (D) Kaplan-Meier survival curves. Significant differences between groups, as identified by a log-rank (Mantel-Cox) test, are indicated in the graph. Two mice from the i.m.-vaccinated group challenged with HALo H5N1 influenza virus died on day 6 postchallenge (66% overall survival). ns, not significant; *, P < 0.05; **, P < 0.005; ***, P < 0.0005; ****, P < 0.0001.