Evaluation of the immune responses against reduced doses of Brucella abortus S19 (calfhood) vaccine in water buffaloes (Bubalus bubalis), India

•Study compared three reduced doses with standard dose of B. abortus S19 vaccine.•Five each female buffalo calves vaccinated with four graded doses of S19 vaccine.•Dose dependent magnitude of immune responses and persistence of antibody observed.•Immune responses in 1/10th reduced dose was comparable to standard dose in buffaloes. Brucella abortus S19 is the most widely used vaccine for the prevention of bovine brucellosis which remains the reference vaccine to which many other vaccine/s are compared. Considering the larger vaccination coverage by reduced dose of vaccine, the study aimed to compare reduced graded doses (1/10th, 1/20th and 1/100th) with standard dose of S19 vaccine (40 × 109CFU /dose) to determine the effective immunizing dose in water buffaloes. A total of 25 female buffalo calves (Bubalus bubalis) in the age group of 4–5 months were equally grouped into five animals each in four test and one control groups and given with specified vaccine dose. The blood samples were collected on post vaccination days 14, 28, 45, 60, 90 and 120 for assessing innate (TNF-α and IL-12), humoral (IgG antibodies against Brucella LPS) and cell mediated immune responses (IFN-γ, CD4 + and CD8 + counts). The full dose, 1/10th and 1/20th reduced doses of S19 vaccine was capable of eliciting pathogen-specific antibody response, vaccine induced secretion of IL-12, TNF-α and IFN-γ with CD4 + and CD8 + effector T cell responses. Persistence of antibody and magnitude of immune responses were found dose dependent. Comparable immune responses were noticed with 1/10th reduced dose similar to standard dose. With this observation, decline of antibody titre will reduce the number of false positives and reduced dose of vaccine will facilitate larger vaccination coverage in the country.