Conclusions This work developed an efficacious and safe vaccine against. s.iniae infection in farmed groupers. The vaccine produced a detectable specific antibody that offered protection against S.iniae infection for at least 6 months. Mortality of vaccinated groupers remained below 2%, while RPS exceeded 97%, implying that groupers treated with the tested vaccine mounted a protective immune response against S. iniae. Moreover, the tested vaccine significantly elevated innate and adaptive immune responses, and regulated the expression of immune-related genes.