Lineage 1 porcine reproductive and respiratory syndrome virus attenuated live vaccine provides broad cross-protection against homologous and heterologous NADC30-like virus challenge in piglets

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen that endangers the swine industry worldwide. Recently, lineage 1 PRRSVs, especially NADC30-like PRRSV, have become the major endemic strains in many pig-breeding countries. Since 2016, NADC30-like PRRSV has become the predominant strain in China. Unfortunately, current commercial vaccines cannot provide sufficient protection against this strain. Here, an attenuated lineage 1 PRRSV strain, named SD-R, was obtained by passaging NADC30-like PRRSV strain SD in Marc-145 cells for 125 passages. Four-week-old PRRSV-free piglets were vaccinated intramuscularly with 10 5.0 TCID 50 SD-R and then challenged intramuscularly (2 ml) and intranasally (2 ml) with homologous NADC30-like PRRSV SD (1×10 5.0 TCID 50 /ml) and heterologous NADC30-like PRRSV HLJWK108-1711 (1×10 5.0 TCID 50 /ml). The results showed that 5 of 5 immunized piglets had a perceptible humoral immune response to vaccination and did not develop fever or clinical diseases after NADC30-like PRRSV challenge. Additionally, compared to challenge control piglets, vaccinated piglets gained significantly more weight and showed much milder pathological lesions. Furthermore, the viral replication levels of the immunized group were significantly lower than those of the challenge control group. These results demonstrate, for the first time, that lineage 1 PRRSV SD-R is a good candidate for an efficacious vaccine against NADC30-like PRRSVs.