Efficacy of Brucella abortus S19 and RB51 vaccine strains: A systematic review and meta‐analysis

Abstract

This systematic review and meta-analysis aimed to recalculate the efficacy of Brucella abortus S19 and RB51 vaccine strains and discuss the main variables associated with controlled trials to evaluate bovine brucellosis vaccine efficacy (VE). The most commonly used vaccine strain was S19, at a dose of 10 10 colony forming units (CFU), followed by RB51 at 10 10 CFU. The most commonly used challenge strain was B. abortus 2308, at a dose of 10 7 CFU, by the intraconjunctival route. Regarding 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 VE. Regarding protection against abortion (n = 15 trials), the S19 vaccine at 10 9 CFU exhibited the highest protection rate (RR = 0.25, 95% confidence

Facing the Human and Animal Brucellosis Conundrums: The Forgotten Lessons

“…Through this methodology, inactivated vaccines are superior to the live reference vaccines [ 144 ], a conclusion that disregards why these vaccines were discarded many years ago [ 35 , 145 ]. Other meta-analyses “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 …” and that the study “provides very relevant information for brucellosis control and eradication … that can drive adjustments in vaccination schemes and brucellosis control modelling” [ 146 ]. Nevertheless, the “prevention of abortion” by itself (i.e., without bacteriological results proving the absence of brucellae) is counterproductive ( Table 2 ).…”

Efficacy of bovine brucellosis vaccines: Conceptions, challenges and meta‐analysis. Response to the Letter to the Editor concerning “Efficacy ofBrucella abortusS19 and RB51 vaccine strains: A systematic review and meta‐analysis” by Blasco et al (Transbound Emerg Dis; 2021: https://doi.org/10.1111/tbed.14259)

“…The letter also argues that the meta-analysis by Oliveira et al (2021) "draw valid conclusions from extremely heterogeneous data". In fact, the biggest challenge in conducting a meta-analysis is grouping the data to prevent bias and maximize accuracy.…”

“…Furthermore, the studies from Plommet et al (1976) and Poester et al (2006) were not directly compared, as they were included in different meta-analysis subgroups: S19 10 10 and RB51 10 10 , respectively (Figures 5 and 6 of Oliveira et al, 2021). The vaccine efficacy of meta-analysis subgroups (summarized data) of those that showed significant risk ratios (RR) were compared (Fiigure 7 of Oliveira et al, 2021), not individual trials or studies directly.…”

“…Furthermore, the studies from Plommet et al (1976) and Poester et al (2006) were not directly compared, as they were included in different meta-analysis subgroups: S19 10 10 and RB51 10 10 , respectively (Figures 5 and 6 of Oliveira et al, 2021). The vaccine efficacy of meta-analysis subgroups (summarized data) of those that showed significant risk ratios (RR) were compared (Fiigure 7 of Oliveira et al, 2021), not individual trials or studies directly. Additionally, from the study conducted by Poester et al (2006) only the 12 animals that were vaccinated while non-pregnant were included in the meta-analysis, as can be seen in Fiigures 5 and 6 from Oliveira et al (2021).…”

“…The vaccine efficacy of meta-analysis subgroups (summarized data) of those that showed significant risk ratios (RR) were compared (Fiigure 7 of Oliveira et al, 2021), not individual trials or studies directly. Additionally, from the study conducted by Poester et al (2006) only the 12 animals that were vaccinated while non-pregnant were included in the meta-analysis, as can be seen in Fiigures 5 and 6 from Oliveira et al (2021). Regarding the recovery of RB51 from the vaccinated animals by Poester et al (2006), it is important to mention that RB51 is eliminated by 12 weeks after vaccination (3 months; Cheville et al, 1993Cheville et al, , 1996 in vaccinated heifers and that it was recovered only from 2/5 animals vaccinated at 6 months of pregnancy at full gestation (Palmer et al, 1997).…”