We next evaluated the prophylactic window of protection against PICV infection using the 10 8 pfu dose of DEF201. Animals were treated one or two weeks prior to challenge with a lethal dose of PICV. Consistent with the trend observed in initial dose titration study, hamsters treated with the 10 8 pfu dose of DEF201 had significantly reduced weights compared to those that received the rAd EV and placebo control treatments ( Figure 3A) . Nevertheless, the pretreatment with DEF201 seven days before infection was highly protective (90% survival rate; Figure 3B ). Notably, the single hamster that failed to survive the challenge succumbed on day 5, which was several days before the mean time to death measured in both the placebo and rAd EV groups. An autopsy to determine the cause of death was not performed.