No, I think plants that are engineered to produce vaccines are a horrible idea. How will you know how much to eat? How will you know how much each banana has produced? Not all will produce the same amount.
I do think that plants that are fortified with certain vitamins can be a great idea for developing countries, though. If you can get the boost of 4 apples in one, why not? We do it with power bars all the time.
Monsanto products should be banned. Too bad we're not willing to pay more for not-so-beautiful produce...