Is there an immunization for poison oak/ivy?

No: Years ago there was a shot that was given and claimed to minimize or prevent poison ivy. Studies never could verify that it worked. In any case, it has not been produced for years, and nothing has taken its place.

Indians ate it: It has been reported that some native americans ingested the plant in the past and were able to orally desensitize themselves. However, apparently this practice has a pretty high risk of causing pruritus ani.