This systematic review and meta-analysis aimed to recalculate the efficacy of these two vaccine strains, and to discuss the main variables associated with controlled trials to evaluate bovine brucellosis vaccines efficacy. The most used vaccine strain was S19, at the dose of 10 ¹⁰ colony forming units (CFU), followed by the vaccine strain RB51 at 10 ¹⁰ CFU. The most used challenge strain was B. abortus 2308, at the dose of 10 ⁷ CFU by intraconjunctival route. For the meta-analysis, trials were grouped according to the vaccine strain and dose to recalculate protection against abortion (four groups) or infection (five groups), using pooled risk ratio (RR) and vaccine efficacy (VE). For protection against abortion (n = 15 trials), S19 vaccine at 10 ⁹ CFU exhibited the highest protection rate (RR = 0.25, 95% CI: 0.12 to 0.52; VE = 75.09%, 95% CI: 48.08 – 88.05), followed by RB51 10 ¹⁰ (RR = 0.31, 95% CI: 0.16 to 0.61; VE = 69.25%, 95% CI: 39.48 – 84.38). For protection against infection (n = 23 trials), only two subgroups exhibited significant protection: S19 at 10 ⁹ CFU (RR = 0.28, 95% CI: 0.14 to 0.55; VE = 72.03%, 95% CI: 57.70 – 81.50) and RB51 at 10 ¹⁰ CFU dose (RR = 0.43, 95% CI: 0.22 to 0.84; VE = 57.05%, 95% CI: 30.90 – 73.30). In conclusion, our results suggest that the dose of 10 ⁹ CFU for S19 and 10 ¹⁰ CFU for RB51 are the most suitable for the prevention of abortion and infection caused by B. abortus.