(A) Body weight changes and survival rates of mice challenged with influenza virus. Mice were immunized twice with 104, 105, or 106 PFU of the PB2-RSVF virus or controls (formalin-inactivated PR8 [FI-PR8] virus and PBS). Two weeks after the boost immunization, mice were challenged with 10 MLD50 of PR8 virus. Body weight (upper panel) and survival (lower panel) were monitored daily for two weeks. (B) Body weight changes and survival rates of mice challenged with RSV. Mice were immunized twice with 104, 105, or 106 PFU of the PB2-RSVF virus or controls (heat-inactivated RSV [HI-RSV] and PBS). Two weeks after the boost immunization, mice were challenged with 106.5 TCID50 of RSV. Body weight (upper panel) and survival (lower panel) were monitored daily for two weeks. Values are expressed as mean changes in body weight (n=3). Bars represent SD.