Subunit vaccines are considered one of the next-generation vaccines. They consist of pieces of a pathogen, instead of the whole organism. Evidently, this also means they do not contain any live pathogen and thus show significantly lower immunogenicity. The immunogenicity of the subunit vaccines can be improved by several factors, e.g. addition of adjuvants, choice of different delivery systems, usage of multiple antigens or epitopes, and optimisation of vaccine dosage.