High SVR12 rates were achieved irrespective of the use of ribavirin or extension of the treatment duration from 12 to 18 weeks ; SVR12 rates ranged from 90 % ( 95 % CI 74-98 ; 28/31 ; cohort 1 , 12 weeks , ribavirin-containing ) to 100 % ( 95 % CI 89-100 ; 33/33 ; cohort 2 , 18 weeks , ribavirin-containing ) .