None of the three PML cases occurred in patients taking Tysabri in monotherapy, other than the one patient who had been on immunosupressants for a protracted period of time. Although some argue that the immunosuppressed patient had been off those drugs for months, there is no proof that his immune system was functioning normally at the time of his Tysabri infusions.

Every day, the 1:1000 figure becomes more outdated, as thousands of new patients begin Tysabri infusions. I would guess that, should the trend of PML-free therapy continue for a year, many more people will begin to believe in the safety of Tysabri.