The present invention relates to Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) mutant strains having increased stability compositions containing the strains or antigens derived therefrom vaccines containing the strains, including killed, attenuated or subunit vaccines nucleic acids encoding PRRSV polypeptides, polypeptides encoded by the nucleic acids, including antigenic fragments thereof antibodies which specifically bind to said polypeptides, and methods making and using thereof.
