Experimental reproductionof severe disease with HP-PRRSV isolates and virus derived from HP-PRRSV clones demonstrated thecausal role of this virus. Recently, partial heterologous protection has been reported for Type 1 and Type2 attenuated PRRSV vaccines against challenge by different Chinese HP-PRRSV isolates providing somehope for reducing economic loss. This paper reports the efficacy of a commercially available Type 2attenuated vaccine in young pigs against heterologous challenge with a Chinese and Vietnamese HP-PRRSV isolate. When compared to unvaccinated pigs, vaccination decreased the length of viremia andviral titer, diminished the time of high fever and reduced macroscopic lung scores following homologousand heterologous PRRSV challenge. These results demonstrate the potential use of vaccine as an aid inthe control of HP-PRRSV outbreaks.©