Particularly, the methylotrophic yeast H. polymorpha should be considered for production of chimeric VLP vaccine candidates since it is already established as a safe and reliable microbial cell factory for the production of biopharmaceuticals like hepatitis B VLP vaccines [51,69,70] or recombinant products that have been granted “generally recognized as safe” (GRAS) status. This evidence concerns the gene PPIB and hepatitis A virus infection.