Antiviral vaccines classically were composed of attenuated or inactivated whole virions produced by infection of eukaryotic cells. With the advent of recombinant DNA (rDNA) technology, the strategy for vaccine production has changed dramatically. The gene(s) encoding a specific protein(s) containing the virus neutralizing site(s) can be isolated and transfected into bacteria, yeast or mammalian cells in culture. These transfected or recombinant organisms or cells can be exploited to produce large quantities of the specific protein which subsequently can be developed in a highly purified form for use as a subunit vaccine. The issue which we would like to discuss is the selection of the host used for the expression of recombinant subunit vaccines.