A live vector vaccine is a vaccine that uses a chemically weakened virus to transport pieces of the pathogen in order to stimulate an immune response.
The genes used in this vaccine are usually antigen coding surface proteins from the pathogenic organism. They are then inserted into the genome of a non-pathogenic organism such as adenovirus where they are expressed on the cell's surface and can elicit an immune response.
An example is the hepatitis B vaccine, where Hepatitis B infection is controlled through the use of a recombinant vaccine, which contains a form of the hepatitis B virus surface antigen that is produced in yeast cells. The development of the recombinant subunit vaccine was an important and necessary development because hepatitis B virus, unlike other common viruses such as polio virus, cannot be grown in vitro.