The invention relates to a fusion protein comprising a HIV gag polypeptide or a functionally equivalent variant thereof and an immunogenic polypeptide, wherein the immunogenic polypeptide is located N-terminal to the HIV gag polypeptide or to the functionally equivalent variant thereof, to a polynucleotide, a vector, a host cell and an immunogenic composition or vaccine composition and the their use in medicine, particularly in in the prevention and/or treatment of a disease caused by an infection in a subject, wherein the infection is by a pathogen which contains the immunogenic polypeptide forming part of the fusion protein or a region thereof.