The present invention relates to an immunogen-carrier, wherein the immunogen-carrier is preferably a virus-like particle (VLP) composed of a plurality of a modified PCV2 ORF2 protein. In particular, the present invention belongs to the field of compliance markers and marker vaccines which allow for the differentiation between infected and vaccinated individuals. In particular, it relates to a compliance marker for vaccines including a subunit antigen, and a DIVA (Differentiating Infected from Vaccinated Animals) system which makes it possible to differentiate between animals infected with a pathogen and animals treated with a subunit antigen derived from said pathogen.