Effective vaccination against porcine reproductive and respiratory syndrome (prrs) virus prior to weaning

A method for inducing a protective immune response in a porcine animal against infection by a Porcine Reproductive and Respiratory Syndrome (PRRS) virus, the method comprising administering to said animal, prior to weaning, a vaccine comprising:

• (a) a modified live PRRS virus, (b) an infectious RNA molecule encoding said modified PRRS virus, (c) an isolated polynucleotide molecule comprising a DNA sequence encoding said infectious RNA molecule, (d) a viral vector comprising said infectious RNA molecule, or (e) a viral vector comprising said isolated polynucleotide molecule;
• and a carrier suitable for veterinary use;
• wherein said vaccine is administered to said animal prior to weaning;
• wherein said modified PRRS virus is prepared by attenuating a virulent PRRS virus on permissive mammalian cells exogenously expressing porcine CD163 receptor, wherein said modified PRRS virus exhibits reduced virulence in said animal in comparison to a wild-type or unmodified PRRS virus from which the modified virus was derived;
• and wherein said administration induces a protective immune response in a porcine animal against infection by a wild-type PRRS virus, wherein said protective immune response provides a reduction in mortality in comparison to an unvaccinated animal infected with PRRS.