Effects of BCG vaccination against Bovine Tuberculosis: a systematic review and meta-analysis Date

Despite the effective control of Bovine Tuberculosis (bTB) in many countries using test-and-slaughter, more than 50 million cattle are still likely to be infected worldwide, highlighting the urgent need for alternative interventions such as vaccines to reduce disease burden and control spread of bTB. Vaccination may be particularly important in regions where the disease is endemic, and test-and-slaughter is neither practical nor acceptable socio-economically. Bacillus Calmette-Guérin (BCG) has been in experimental use in cattle for over a century, however there is lack of thorough understanding of its efficacy for implementation as part of future bTB control programs. Here, we performed a systematic review and meta-analysis of the protective efficacy of BCG against bTB in cattle in accordance with PRISMA guidelines. Based on a random-effects (RE) model, the analysis estimated a relative risk (RR) ratio of infection of 0.76 (95% CI: 0.70, 0.83) for vaccinates compared to controls, corresponding to a direct vaccine efficacy of 24% (95% CI: 17, 30). Our analyses report a small but protective direct effect of BCG in cattle that may translate to a significant impact at the population level when indirect effects are considered.