I was on copaxone. During the time I was on copaxone my MS get worse. More liesons and the ones I had grew twice the size. Since my liesons are at the C2 andC3 you can see the dangers of this disconnect. So my Doc put me on Tysabri. In six months no new liesons and the ones I had got smaller. So for me, I love it. Never had a bad reaction. And the treatment itself only takes about 2 hours every 28 days, during which time I sleep. As far as PML, well the JC virus is measured by a numerical value. So they monitor that along with other signs very closely through blood work. I personally love the stuff.

4 years on Tysabri, JC negative, no problems, betaseron first drug made me want to die, that was my first neuro, MS neuro said get off that crap and put me on Tysabri. I tried tecfidera and it was crap. Back on Tysabri, no issues, no progression. That's really what the DMDs are all about, no new lesions. So, take the medication that has the highest effective rate, currently Tysabri, without the flu like symptoms or the flushing and stomach issues, etc. If you flip to positive, then switch.

I almost died from tysabri in march of this year due to an acute hypersensitivity reaction.
Everyone is different, however, every ms med I have been on so far (5+ and counting) has not had very good outcomes. My body just cannot handle them.
Since March, I have not been on any of the 12 wonderdrugs....and I feel 100x better, however, it is only hurting me in the end because nothing is slowing the progression of my disease....
Best advice- weigh your options, educate educate educate.

It has helped me out tremendously!! Am I 100%, no, but I don't think I'd have made the improvements I have without it. If you are positive for JCV and it is low enough, you can still take it. I would not be where I am if I had stayed on Avonex. My dr felt that he wanted to "knock down the MS" aggressively and then switch to something else to keep me at that level. The first 2 years your risk of PML is the same as someone that is negative for it. I think it's worth it and I am grateful my dr put me on it.