Journal of Vaccine Research 2024, Vol.14, No.1, 27-31 http://medscipublisher.com/index.php/jvr 29 Table 1 estimated the vaccine efficacy of the BCG vaccine in cattle. Evaluated through different diagnostic tests such as IGRA (DST 1), skin tests (DST 10), and visible lesions, the 95% credible intervals (CrI) for overall efficacy (VET) were 74% to 96%, 55% to 94%, and 1% to 47%, respectively, demonstrating the vaccine's direct (VED) and indirect (VEI) efficacy in reducing the transmission of bTB. The IGRA test showed the highest overall vaccine efficacy at 89%. This indicates that the BCG vaccine not only directly reduces the infection rate among the tested cattle but also indirectly lowers their risk of transmission. Table 1 Estimated vaccine efficacy for BCG in cattle by mode of action Diagnostic test End-point efficacy Transmission rate efficacy - Total efficacy (95% Cl) Direct efficacy (VED) (95%Crl) Indirect efficacy (VEI) (95%Crl) Total efficacy (VET) (95%Crl) DST 1 (IGRA) 39 (22 to 54) 58 (34 to 73) 74 (46 to 89) 89 (74 to 96) DST 10 (skin) 40 (19 to 57) 46 (14 to 66) 67 (39 to 87) 82 (55 to 94) Visible lessions 25 (1 to 57) - - - Table 2 presents the estimated experimental reproduction ratios (R) for bovine tuberculosis (bTB) within a year and the posterior probabilities of R<1 for different combinations of vaccination statuses (seeder-sentinel pairs). In the unvaccinated control group (unvaccinated-unvaccinated), the R value was 3.1, with no probability of achieving the disease control threshold of R<1. When unvaccinated seeders were paired with vaccinated sentinels (unvaccinated-vaccinated), the R value decreased to 1.3, with a posterior probability of R<1 being 0.075. For combinations of vaccinated seeders with unvaccinated sentinels (vaccinated-unvaccinated), the R value further decreased to 0.8, with the posterior probability of R<1 increasing to 0.72. In pairs of vaccinated seeders with vaccinated sentinels (vaccinated-vaccinated), the R value dropped to the lowest at 0.3, with a posterior probability of R<1 being 1, indicating that vaccination significantly reduces disease transmission and could potentially lead to disease control. Table 2 Estimated experimental reproduction ratios by vaccination type of sentinel and seeder animals Seed Sentinel pair R(1-year contact) (95% Crl) Posterior probability that R<1 Unvaccinated-Unvaccinated 3.1 (2.3 to 4.1) 0.0 Unvaccinated-Vaccinated 1.3 (0.9 to 1.8) 0.075 Vaccinated-Unvaccinated 0.8 (0.4 to 1.5) 0.72 Vaccinated-Vaccinated 0.3 (0.1 to 0.7) 1.0 Figure 3 provides scenario analyses for the prospective use of bovine tuberculosis (bTB) vaccines in the Ethiopian dairy sector. Panel A illustrates the transmission rates of bTB within cattle herds around Addis Ababa and in emerging dairy belts in Hawassa, Mekelle, and Kombolcha, calibrated based on herd-level prevalence data collected from these areas. Panel B shows that the estimated prevalence of bTB within herds ranges widely (5.8% to 78%), with the basic reproduction ratio R0 estimates also displaying similar heterogeneity, with no clear correlation to geographical location or herd size. Panel C uses cattle movement data models collected from Gondar, Mekelle, and Hawassa to predict the evolution of bTB prevalence over the next 50 years. These predictions include scenarios without vaccination (pink), with estimated direct vaccine efficacy at 58% (light blue), and with additional indirect effects at 74% (purple). These projections demonstrate the potential impact of different vaccination strategies on controlling the prevalence of bTB. 2 Analysis of Research Findings This study on the impact of the BCG vaccine against the transmission of bovine tuberculosis (bTB) showcases the significant potential of the BCG vaccine in reducing bTB transmission through field trials conducted in Ethiopia. The research employed an innovative natural transmission experimental design, placing both BCG-vaccinated and unvaccinated cattle herds in the same environment to directly observe the vaccine's effect on bTB transmission. The results indicated a marked reduction in bTB transmission rates among vaccinated herds, not only revealing the direct protective effect of the BCG vaccine on vaccinated animals but also highlighting its potential to reduce
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