Improved Vaccines by Using Molecular Biotechnology Techniques -Novel, safer vaccines may be another product of cloned genes. Usually, vaccines are made from whole viruses that have been either killed or weakened so that they can no longer cause disease but can still stimulate the body's immune defences.

The problem is that sometimes these viruses are not killed or are not weakened enough, thus they end up causing the disease and sometimes even death.

The first successful subunit vaccine was produced for hepatitis B virus (HBV), which infects the liver. Initial attempts to produce the HBsAg protein in E coli failed, so researchers turned to yeast. The HBsAg gene was inserted into a high copy yeast expression vector.