In the time I have been taking Tysabri, they have obtained much more data, as more and more people began taking
Tysabri and staying on it longer. The
JC virus test has been very helpful, allowing people who are negative to go on Tysabri with much less worry of PML, as well as giving people who test positive a better idea of the risks and allowing them to make more informed choices and decisions.
At this time, they have identified 3 main risk factors for PML while on Tysabri:
1.