ABSTRACT
A subunit vaccine uses only those antigenic fragments of a microorganism that are best suited to stimulating a strong immune response. The genes for these protein subunits can be introduced into the genome of a bacterium or yeast by the genetic engineering techniques. These subunits are produced in quantity by the bacterium or yeast and are then harvested in pure form for use as a subunit vaccine. For example, the latest hepatitis B vaccine is a subunit vaccine produced in a yeast. The vaccinia virus used to control and eradicate smallpox has also been genetically engineered to express the antigens of other viruses.
