Porcine reproductive and respiratory syndrome virus (PRRSV) compromises pig performance.However, increasing standardized ileal digestible Lys per Mcal metabolizable energy (SID Lys:ME) above requirement has been shown to mitigate reduced performance seen during a PRRSV challenge. The objective of this study was to evaluate the effects of increasing the dietary SID Lys:ME from 100% National Research Council (NRC) requirement to 120% of the requirement in vaccinated (vac+; modified live vaccine [MLV] Ingelvac PRRS ® ) and nonvaccinated (vac-; no PRRS vaccine) grower pigs subjected to a PRRSV challenge. In addition, the dietary formulation approach to achieve the 120% ratio by increasing Lys relative to energy efficiency was not impacted (P > 0.10) by treatment in the vac-pigs. In summary, PRRSV challenged grower pigs consumed feed to meet their energy needs as indicated by the increase in ADFI when energy was diluted in the (LE) diet, compared to control pigs. In both PRRS vac+ and vac-pigs subsequently challenged with PRRSV, regardless of formulation approach, fed 120% SID Lys:ME diets resulted in enhanced overall growth performance.