Fig. 4
Virus challenge studies in mice. a Mice (n = 4–5) received 200 µL of pooled sera intraperitoneally (i.p.) and were challenged intranasally (i.n.) with 5 mLD50 of X-31 (a reassortant virus with the hemagglutinin (HA) and neuraminidase (NA) of A/Hong Kong/1/1968 and the internal proteins of PR8) or X-79 (a reassortant virus expressing HA and NA of A/Philippines/2/1982 and the internal proteins of PR8). Weight and survival were observed for 14 days postinfection. b–e Weight curves (b, d) and survival curves (c, e) of mice challenged with the indicated viruses. The weight curves show the mean with SD. In the survival plots, the proportion of surviving animals in each group is shown in parentheses and statistical significance was inferred by log-rank Mantel–Cox tests against the Mock groups (DNA prime only or untreated) with *P ≤ 0.05 and **P ≤ 0.01
