Having observed dramatic protection when administered up to 2 weeks prior to challenge, a final experiment was conducted to determine the therapeutic value of DEF201 in the hamster PICV infection model. When DEF201 was administered 6 or 24 h after challenge, highly significant protection was observed ( Figure 5 ). Efficacy waned when DEF201 treatment was delayed to 48 h postinfection. As anticipated, the treatment given 24 pre-challenge verified previous activity, with all animals surviving challenge.