MS is a minefield of information for the newly diagnosed. There is just so much it’s impossible to instantly get to grips with it.
To start with, any disease modifying drug (or DMD) is designed to prevent relapses and reduce the severity of relapses. And Tecfidera is a very good first line DMD to start with. On average it reduces relapses by about 50%. As for how successful it is, it’s impossible to prove in the case of an individual.
If you reduce relapses, then you are also reducing the damage caused to the myelin. This is the substance that coats the nerves of your central nervous system.
Reducing the damage to myelin should reduce the potential disability. But it won’t change the rate at which, or the likelihood of your RRMS becoming secondary progressive.
Not everybody with RRMS becomes SP. many do not. But as you are aware, it’s possible. It tends to be some years in before SP takes over. And some people are glad of it (me for one). The reason an individual might be happy to become progressive is if they’ve had lots of disabling relapses. The thought of having no more relapses, maybe just gentle progression (hopefully) is a good one.
As a person who didn’t have the range of DMDs you do now, and being intolerant of those I’ve tried, I had a lot of relapses and became quite disabled.
In your case, hopefully Tecfidera will do it’s job well, you’ll have few relapses and you’ll remain well.