Efficacy of Brucella Vaccines in Sheep: A Systematic Review and Meta-Analysis

Background. Brucellosis is a major worldwide public health problem with economic and zoonotic implications. Despite the importance of vaccines in preventing brucellosis, no previous systematic evaluation of vaccination in sheep has been conducted. Materials and Methods. Articles were searched in databases such as PubMed, Science Direct, Cochrane, VIP, Wan Fang, and CNKI by screening the articles, and articles reporting Brucella vaccination in sheep were included in the study. Meta-analysis was performed using random effects models to calculate pooled risk ratios for vaccines and to calculate vaccine effectiveness. Results. A total of 2,605 articles were retrieved, and 17 articles were obtained through screening for analysis. The effectiveness of vaccination was 65% (RR = 0.35, 95% CI: 0.27-0.36; VE = 65%), with the M5 vaccine being significantly more effective at 84% (RR = 0.1587, 95% CI: 0.0256-0.9858; VE = 84%) than the other vaccines, and intramuscular injection could be the best route of immunization. Rev.1 was indicated for female sheep, especially for pregnant ewes (RR = 0.2016, 95% CI: 0.1139-0.3569; VE = 80%), and for reduced abortions (RR = 0.0978, 95% CI: 0.0459-0.2085). Conclusion. This meta-analysis was conducted to identify the relevant factors affecting vaccine efficacy. We recommend that sheep be inoculated intramuscularly with Rev.1, different inoculation protocols be adopted for sheep of different ages, and pregnant ewes be inoculated with Rev.1 to prevent abortion.