Hi Annabel,
You're going to get a lot of advice here, with many different opinions. My apologies for Antone. We don't usually attack or get attacked around here. Sometimes there are those who feel like "The Man" (doctors) are keeping some great secret from them, or are just feeling very bitter. Again, my apologies.
I know you're here because you're concerned about your dad. He's got a great daughter. There is no one perfect cure that's right for everyone. My personal experience is this:
I am an assistant in a pediatrics office. In ten years time I have never brought home a single germ. Anything I've ever caught, I've caught it from my kids. That's because I'm closer to them on a daily basis. I personally haven't ever caught anything while on Enbrel. Again, it's a matter of diligent handwashing, not sharing lollipops, that sort of thing.
Whatever your dad does, understand that he'll eventually have to trust in something, if he's going to spend any pain-free days with his lovely daughter. Vitamin A, in sufficient quantities, can stop a heart. Everything has it's risks. Even breathing. All you can do is be there for him, and have a little Faith.
