Characterization of humoral and cellular immune responses elicited by reduced doses of Brucella abortus S19 (calfhood) vaccine in cattle calves of India

Brucella abortus S19 vaccine is a stable attenuated smooth strain, globally used as calfhood vaccine for the prevention of bovine brucellosis. Various agencies demonstrated different doses for vaccinating cattle and buffalo calves leading to ambiguity in selecting a suitable immune vaccine dose. The current study aimed at evaluating four graded doses of S19 vaccine to arrive at the dose which could produce comparable effectiveness as that of full dose prescribed by Indian Pharmacopeia among the Indian calves. Four vaccine doses of which the first dose consisted of full dose (40 × 109 CFU/dose) and the other three were 1/10th, 1/20th, 1/100th reduced doses along with control were tested. Each vaccine dose was administered to 13 cattle calves of 4–5 months of age maintained in separate groups. The blood samples were collected on 0 to 240 days post-vaccination (DPV) at the intervals of 0, 14, 28, 45, 60, 90, 150, 180 and 240 for assessment of vaccine-induced innate, humoral and cell-mediated immune responses. The sero-conversion of all vaccinated animals on DPV 45 and persistence of antibody till DPV 240 were noticed. No significant differences were observed in antibody response between animal groups that received full and 1/10th reduced doses. Innate and cell-mediated response by IL-6, TNF-α¸ IFN-γ, CD4+ and CD8+ cell counts showed dose-dependent responses with no significant difference between full dose and 1/10th reduced doses. The results suggest a possible one log reduction of full dose without compromising immune responses to aid larger vaccination coverage for creating herd immunity.