“…First, the genetic diversity of PRRSV affected the efficacy of MLV, especially in humoral immunity, which offered better protection against antigenically homologous strains than against heterologous strains [8,17,18,22,24]. However, the protection of cellular immunity between homologous and heterologous strains was depended on the number of virusspecific interferon-c producing cells [3,22,23,33,47]. In Taiwan, three kinds of PRRSV vaccines have been used, including two MLV and one subunit vaccine.…”