Vaccines and methods for making and using the same. An example vaccine may be a vaccine against enterotoxigenic Escherichia coli. The vaccine may include an Escherichia coli strain. The Escherichia coli strain may produce K88 fimbria and a fusion protein including a mutant LT enterotoxin linked with a STb enterotoxin. An example method for producing a vaccine for porcine post-weaning diarrhea may include providing a first strain of Escherichia coli. The strain may include the eltAB gene and the estB gene. The method may also include amplifying the eltAB gene, mutating the eltAB gene, generating a genetic fusion of the mutant eltAB gene with the estB gene, and transforming a second strain of Escherichia coli with the genetic fusion.