The present invention relates to nucleic acids comprising:(a) sequences of a replication competent transmissible gastroenteritis virus (TGEV), which sequences encode a TGEV replicase under the control of expression regulatory sequences, wherein the replicase is expressed in a host cell and will initiate replication of the nucleic acid and thus increase the number of nucleic acids in the cell and(b) a sequence encoding at least one neutralizing epitope of ORF5 of porcine reproductive and respiratory syndrome virus (PRRSV), which sequence includes a disulfide bridge forming residue and(c) a sequence encoding at least one further polypeptide capable of increasing an immune response against PRRSV.The present invention further relates to vectors, virus particles and host cells comprising these nucleic acids as well as their use for the preparation of vaccines, specifically for the preparation of vaccines.
