siRNA synthesized in vivo induce antiviral response in suckling mice and promote survival after FMDV infection. Suckling mice were challenged by subcutaneous injection in the neck with 20 LD₅₀ of HKN/2002 (A) or 20 LD₅₀ of YNBS/58 (B) after 6 h of treatment with either control plasmids or FMDV-specific siRNA-expressing plasmids. All animals were observed for 6 days after challenge.