Average daily gain (ADG) and viral load (VL) were evaluated for pigs co-infected with porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) and porcine circovirus type 2b (PCV2b). Pigs were pre-selected for WUR genotype (a marker on chromosome 4 associated with weight gain and VL under PRRSV-challenge), half were vaccinated for PRRS, and half were not. Results indicate that vaccination for PRRS resulted in slower growth prior to co-infection and that the AB WUR genotype was associated with faster growth prior to co-infection, lower PRRS VL, and lower PCV2b VL in vaccinated pigs.