Studies of NAb development have shown that NAbs develop early in IFN-b therapy. A study by the IFNB Multiple Sclerosis Study Group reported "[t]he percent of patients NAb+ in the three treatment arms, by time period, is presented ... indicating that, for the most part, NAb development is a first-year phenomenon."⁸

The percentage of antibody-positive (at least two consecutive titers at 20 NU/ml) patients in the 8-MIU IFN-b-1b treatmentarm was as follows:

0-6 months: 7-12 months: 13-18 months: 19-24 months: 25-30 months:

15% 31% 36% 38% 39%