Vaccinia virus, the world's oldest vaccine, was used originally for the eradication of smallpox. It is now being genetically engineered to create new live vaccines for use against other infectious agents of medical and veterinary importance. Genes coding for antigens of several pathogens have been linked to vaccinia virus transcriptional regulatory signals and inserted into the vaccinia virus genome. The resultant recombinant viruses are infectious, express the foreign gene, stimulate specific immune responses in vaccinated animals and can protect against disease (...) caused by the corresponding pathogen. (shrink)