The invention relates to a strain suitable for producing a live, orally applicable Escherichia coli vaccine for the prevention of post-weaning diarrhoea in pigs, and the procedure suitable for producing that strain. The essence of the strain is that the enterotoxin-free and originally wild-type Escherichia coli strain simultaneously produces two adhesive fimbriae (F4 and F18), whereas the essence of the procedure is that the enterotoxin-producing ability if the wild, pathogenic, enterotoxigenic Escherichia coli strain originally capable of producing enterotoxins and F18 fimbriae is abolished by a genetic intervention while retaining the ability of the strain to produce F18 fimbria facilitating adhesion to the small intestinal wall of weaned piglets, and subsequently the strain thus modified is rendered capable of producing a further surface adhesion fimbria (F4).