Since it sounds like you're at the end of your poison ivy misery, just wanted to pass on my 2c worth. When I was a kid I used to have to get shots all the time...back then I was able to get a shot to prevent catching the following season...but then the other shots after I caught poison ivy...just to be able to breathe.
In just reading this board, I haven't read anything really positive about Zanfel and on top of that...something that's ineffective...pretty pricey.
Anyway, someone else just posted their use of Retin-A. I discovered this a couple years ago and it's the 1st thing I run for now...it's amazing how effective & QUICK it is. I definitely agree with her and hope you give it a try should you catch it again.