I would say no, since vitamin c doesn’t enhance the body’s immune system against a specific disease.

And the new definition seems to be about the same as the old one, to me at least. The only material difference was the removal of “protecting” (I don’t have the specific wording in front of me)

While I can’t attest to what exactly their intent in that deletion was, I can imagine it may have been to remove the temptation to make bad faith interpretations of what “protection” is meant in this context. Clearly though the original context was that vaccines protect us in the same was we mean when we say car seatbelts protect against accidents.