Initially it worked for about 4 months and then gradually got worse each fortnight. Having done a bit of research I asked my GI about moving to weekly injections which has put me back into remission and been brilliant. I had other injuries and joint problems which I think meant my immune system had a lot of 'normal' work to do, so the amount of Humira just wasn't enough to cover it - that's what it felt like. Been fine ever since.
Humira is not quite the same as Remicade, it's fully humanised so the chances of you developing anti-bodies to it is much less. So likely to work longer.