I was put in Imuran to treat my UC a little more than a year ago. I was told by my GI doc and an immunologist/allergist who was overseeing my case to get the flu and H1N1 shot. I am a health care provider, I am immunocompromised and I have a chronic illness, UC. So I took the advice of my trused docs and got both.
All I can say is that shortly thereafter I got very sick and was bed ridden with a fever for 2-3 days. Nothing after that. It's important to note that my childrens brought home some swine flu bug right around that time. My docs told me I just picked it up from them. Those two days sucked, I am usually never sick.
I would do it all over again. I am planning on getting the flu shot ever year from now on.