To test whether favipiravir had efficacy against BRBV-STL in vivo, we inoculated Ifnar1-/- mice via IP route with 4 x 102 pfu of BRBV-STL and treated the mice twice daily with 150 mg/kg of favipiravir in 0.5% methylcellulose via oral gavage for 8 days beginning immediately after infection. This evidence concerns the gene IFNAR1 and infection.