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

A benefit of genetic engineering is the production of valuable proteins that have helped in managing of illness in human beings. Bacteria were genetically engineered to produce proteins of medical importance. One example of such a protein is human insulin which is given the name humulin and is made using E. coli bacteria.Earlier,  insulin from pig cells was used to treat patients with diabetes but many of them could not tolerate it because it has a slightly different arrangement of amino acids from that of humans and so the human body rejects it. Humulin is tolerated by the human body and so many patients are now using it to lead normal lives.