Will Falconer, DVM Moderator
Hey Peter,
This guy should be immune for life, and will only add to that immunity with each (semi-) natural exposure he comes across. The goal is building him up and letting his innate intelligence see the foreigners for what they are, and mounting an appropriate response (not over reacting or under reacting). Knowing all you've done for him, I think you can rest easy that he's capable.
Carry on, good man.