The rates of sustained virologic response were 99 % ( 95 % confidence interval [ CI ] , 96 to 100 ) in the group that received 12 weeks of ledipasvir-sofosbuvir ; 97 % ( 95 % CI , 94 to 99 ) in the group that received 12 weeks of ledipasvir-sofosbuvir plus ribavirin ; 98 % ( 95 % CI , 95 to 99 ) in the group that received 24 weeks of ledipasvir-sofosbuvir ; and 99 % ( 95 % CI , 97 to 100 ) in the group that received 24 weeks of ledipasvir-sofosbuvir plus ribavirin .