What is the purpose of using genetic engineering to create edible vaccines?

What is the purpose of using genetic engineering to create edible vaccines?

A. to create vaccines that are capable of lasting years in the body to prevent future infections
B. to diminish negative side effects that may occur from administering vaccines with syringes
C. to enhance the flavor of vaccines so people are more likely to use them
D. to prevent widespread diseases in developing countries without using syringes