Of 167 patients evaluable for efficacy , 49 ( 29 % ) had MRI disease activity recurrence : 0/45 ( 0 % ) natalizumab , 19/41 ( 46 % ) placebo , 1/14 ( 7 % ) IM IFN -- 1a , 8/15 ( 53 % ) GA , and 21/52 ( 40 % ) MP .