In the first part of the study will examine what experimental vaccine and vaccination are the most effective in non-immune sows and fattening piglets. Of five companies PRRSV isolates will be isolated and expanded in a new PRRSV-sensitive cell and sequenced to be ORF4, ORF5 and ORF6. First 5 will experiment with non-immune animals are performed. In each experiment, the pigs will be vaccinated with either a commercial attenuated vaccine, or a commercial inactivated vaccine, or an experimental inactivated vaccine, based on the five PRRSV isolates (homologous situation). The virological protection will be determined by following the viremia. Afterwards, the experiment will be repeated in pigs with maternal immunity. Final will be determined to give booster serological immune response in sows whether the three vaccines. This study will be an ideal vaccination scheme proposed worden.²