I'm currently taking Kesimpta and was previously on Tysabri. The pamphlet for Kesimpta states PML could develop. My Doctor took me off Tysabri because my JCV number was almost 2.
When I asked about it he stated no one on Kesimpta had developed PML. I wonder how they know it's a risk?
Probably because it's very similar to Ocrevus, which is older, and has had cases of PML. Kesimpta is newer, and they haven't happened, but they could.
Kesimpta is Arzerra, but at a much lower dose. The PML warning is there because it has happened with Arzerra. Kesimpta is one of the safe switch options for those with high JCV levels. They know it's on the label. There have been no cases of PML with Kesimpta.
I've been on Kesimpta for about 3 years now and I love it! I was on Ocrevus when it can out and did that for about 7 years and it was just getting too hard on my body. I have PPMS, but it's been a lot better. PML is just a possibility, although no cases have been reported yet. I wouldn't worry too much about that. I hope this helps?
I also am JCV positive but I never took these kind of MS meds, I took Copaxone & Avonex had side effects, but guess I’m just part of population who were exposed at some point in my life, my level is high, as Neurologist about it b4 starting Kesimpta and said it would be fine. I know ppl who have switched from the med you were on to Kesimpta w/positive JCV and are fine. If you look up John Cunningham Virus you’ll see that about 50% of population are exposed to it w/out knowing or having symptoms, like myself. All will be ok
Kesimpta from Ocrevus?
Kesimpta Question
Kesimpta 
