FIGURE 1.

Safety and protective efficacy of X-31ca against RSV challenge. (A) Mice (n = 4 per group) were vaccinated with 10⁶ PFU of X-31ca and weight changes were observed daily for 2 weeks. (B,C) Mice (n = 4 per group) were vaccinated with 10⁶ PFU of X-31ca and RSV A2 at 2 (–2d Vac), 4 (–4d Vac), 6 (–6d Vac), 14 (–14d Vac), or 28 (–28d Vac) day intervals. Non-vaccinated (No Vac) mice were infected with 10⁶ PFU of RSV A2 only. The body weight was monitored daily (B) and lung viral titer was determined by plaque assay at day 4 p.c. (C). (D) Mice (n = 4 per group) were vaccinated with formalin-inactivated X-31ca and challenged with 10⁶ PFU of RSV A2 2 days later (FI X-31ca Vac). Non-vaccinated mice were infected with 10⁶ PFU of RSV A2 only (No Vac). Lung viral titer was determined by plaque assay at day 4 p.c. The dotted line represents the limit of detection; 100 PFU/g of lung tissue (^∗P < 0.05, ^∗∗P < 0.01 compared with the No Vac control group).