Boussole you are one of the few that posts on this forum that has actually gone away successfully (for a long period of time) while on Humira.
Some quick background on myself. I was on Remicade for many years, from when I was 20-28. I could stretch my every 8 week infusions to 11 or 12 weeks no problem. After college, I worked seasonal jobs, and traveled, extensively around the work for 2-3 months at a time, timing the infusions to happen immediately before and after departure. I was fine.
Then Remicade quit working. For a variety of reasons, I ended up on Cimzia (and I take one every two weeks), and my ability to drop everything and travel ended with it.
As I have noted to my doctors - and something to which they have tacitly agreed - Cimzia and Humira make it very difficult to travel extensively, whether overseas or even in your own country. I'm doing other things now, but still escape for two week stints to third world countries as often as I can, usually injecting with Cimzia just before getting on the plane.
I'm sure the medication can be shipped to you from the US ... you just have to have somewhere to receive it. Also, travel times are longer, so you'll probably have to have it sent from your pharmacy to a friend, who can pack the cooler with more ice (they are typically packed for 48 hours ... that may not be enough) before sending it. This will be expensive.
Others on this list have looked into getting Humira or Remicade overseas ... regardless of the nationalities (whether US getting it in Europe, or Australian going to England, etc) they've found it very difficult as your "home" insurance won't cover it out of country.
However, Boussole's post gives hope for those that want to do this. It is possible.
There are many on this forum that let Crohn's define their life. There's a lot of "I can't because of my Crohn's Disease" around here. It is encouraging to see individuals that have figured out or are trying to figure how to do great things despite their Crohn's Disease. I've had Crohn's for 14 years, and in the last nine years, I've spent probably close to 14-15 months out of the US, mostly in third world countries. To the best of my ability, I do not let Crohn's dictate what I do and don't do. I hope you're able to figure out his logistical challenge and go to Europe long-term.
Finally, I wouldn't worry about the immune response stuff. Yeah, there are a few more nasties out in the third-world ... but I wouldn't worry about it. In my experience, its not a big deal. Regarding immunizations ... the big one that is live (and required for some of South America) is Yellow Fever. You cannot get a Yellow Fever vaccine while on an anti-TNF. It is actually a medication class that qualifies for a Yellow Fever medical waiver. You just need to go to a clinic designated to administer the vaccine, show documentation of the prescription, and they should give you the correct paperwork.