Development and evaluation of the immunoprotective efficacy of a bivalent inactivated vaccine against Streptococcus suis serotypes 2 and 9.

Streptococcus suis (S. suis, SS), a significant zoonotic pathogen, causes large-scale swine epidemics and substantial economic losses. Based on capsule antigen differences, at least 29 serotypes have been identified. Given that existing commercial vaccines target only serotypes 2 or a few others, and lack immunoprotection against serotype 9, this study designed and developed a bivalent inactivated candidate vaccine to cover serotypes 2 and 9, evaluation of the protective efficacy of weaning piglets. The vaccinated piglets were in normal condition without adverse reactions and deaths, indicating that the vaccine was very safe. Experimental vaccine induced significantly higher levels of specific antibodies than the commercial vaccine. Further pathogenicity tests confirmed that the vaccine exhibited 100% immunoprotection efficacy against both Streptococcus suis serotype 2 and serotype 9 strains, and significantly reduced mortality and clinical severity of disease following infection with these two bacterial strains. According to a search of the public literature, this study provides evidence that the bivalent vaccine demonstrates no less than the efficacy of existing commercial vaccines, while exhibiting high safety and superior immunoprotection efficacy, offering a reliable technical solution for the prevention and control of co-infection with Streptococcus suis type 2 and type 9.