hi Faith
as long as you are keeping his immune system strong, especially that in his GIT you should be fine...including of course the supps he needs daily. Be sure to pack those in a zippered bag in your CHECKED baggage or else they will be confiscated by TSA at check in.
with TS change can always be a potential trigger as can excitement, travel stress etc...but we found this quickly waned once the fun of the new place overshadowed it.
hope you have a great trip
Cheri