Efficacy of an inactivated whole-cell injection vaccine for nile tilapia, Oreochromis niloticus (L), against multiple isolates of Francisella noatunensis subsp. orientalis from diverse geographical regions

• Efficacy of an injectable vaccine of Francisella noatunensis subsp. orientalis with adjuvant was tested against challenge with three different Fno isolates in Nile tilapia. • The developed vaccine stimulated innate and adaptive immunity post-vaccination and provided protection against homologous and heterologous Fno isolates. • Significantly higher IgM levels and significantly lower bacterial burden following i.p. vaccination and challenge correlated with protection, suggesting a protective role of antibody-mediated immunity against Fno in Nile tilapia.