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Background <p><i>Brucella abortus</i> strain RB51 is a live attenuated rough vaccine developed to overcome the serological interference of conventional smooth vaccines. Since replacing strain S19 in the United States (1996) and globally thereafter, RB51 has been promoted as a DIVA (Differentiating Infected from Vaccinated Animals) vaccine for brucellosis control in cattle and other livestock. However, conflicting reports on its safety, efficacy, and adverse effects have generated ongoing debate.</p> Methods <p>We conducted a systematic review following PRISMA guidelines. Six electronic databases (PubMed, Scopus, Web of Science, CAB Abstracts, Cochrane Library, SciELO) were searched from January 1990 to March 2025. Studies reporting original data on RB51 vaccination in animals or humans, including safety, efficacy, adverse events, or human health outcomes, were included. Due to extreme heterogeneity (I² &gt; 94%), findings were synthesized narratively without meta-analysis.</p> Results <p>Ninety-four studies (189 individual trials, 8 host species, 25 countries) were included. Positive outcomes included DIVA capability (no serological interference in most experimental settings), consistent Th1-biased cell-mediated immunity (IFN-γ, CD4⁺/CD8⁺ T-cell responses), and efficacy against <i>B. abortus</i> challenge in controlled trials (up to 100% protection). However, substantial adverse effects were documented: abortion rates in cattle ranged from 0.5% to 50% (median 8.3%), with higher rates (6–88%) in bison and elk; placentitis, stillbirth, and premature birth were reported across multiple host species. Vaccine strain shedding in milk occurred in 1.8–6.1% of vaccinated cows and buffaloes (culture-confirmed median 4.0%). Diagnostic interference (atypical seropositivity on smooth-LPS tests) was observed under field conditions, particularly after revaccination. Efficacy limitations included failure to protect against <i>B. melitensis</i>, <i>B. suis</i>, and <i>B. ovis</i>, waning immunity (&lt; 4 years), and no benefit from revaccination. Human health risks included occupational accidental exposures (USA, Brazil, Egypt) and raw milk-associated RB51 infections (USA), complicated by intrinsic rifampin resistance.</p> Conclusions <p>RB51 preserves DIVA capability and induces cell-mediated immunity under ideal conditions but carries significant risks, including vaccine-induced abortion, milk shedding, and incomplete cross-protection. Its safety and effectiveness are highly context-dependent, performing well in low-prevalence countries with robust test-and-slaughter programs but failing in high-endemicity settings where pregnant adults are routinely vaccinated. Strict contraindication of RB51 in pregnant animals, pasteurization of dairy products from vaccinated herds, and complementary use of species-specific diagnostic tests are urgently needed. RB51 should not be used as a stand-alone intervention, and its continued use in endemic regions with mixed <i>Brucella</i> species requires re-evaluation.</p>

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Brucella abortus RB51 vaccination: a comprehensive systematic review of safety, efficacy, and global field outcomes (1990–2025)

  • 期刊论文

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  • 发表日期：

    2026年7月31日

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  • Maryam Dadar,
  • Beatriz Arellano,
  • Jamal Gharekhani,
  • Agustín Rebollada-Merino,
  • Youcef Shahali,
  • Mehran Varnasseri Ghandeali,
  • Fabrizio De Massis

摘要

Background

Brucella abortus strain RB51 is a live attenuated rough vaccine developed to overcome the serological interference of conventional smooth vaccines. Since replacing strain S19 in the United States (1996) and globally thereafter, RB51 has been promoted as a DIVA (Differentiating Infected from Vaccinated Animals) vaccine for brucellosis control in cattle and other livestock. However, conflicting reports on its safety, efficacy, and adverse effects have generated ongoing debate.

Methods

We conducted a systematic review following PRISMA guidelines. Six electronic databases (PubMed, Scopus, Web of Science, CAB Abstracts, Cochrane Library, SciELO) were searched from January 1990 to March 2025. Studies reporting original data on RB51 vaccination in animals or humans, including safety, efficacy, adverse events, or human health outcomes, were included. Due to extreme heterogeneity (I² > 94%), findings were synthesized narratively without meta-analysis.

Results

Ninety-four studies (189 individual trials, 8 host species, 25 countries) were included. Positive outcomes included DIVA capability (no serological interference in most experimental settings), consistent Th1-biased cell-mediated immunity (IFN-γ, CD4⁺/CD8⁺ T-cell responses), and efficacy against B. abortus challenge in controlled trials (up to 100% protection). However, substantial adverse effects were documented: abortion rates in cattle ranged from 0.5% to 50% (median 8.3%), with higher rates (6–88%) in bison and elk; placentitis, stillbirth, and premature birth were reported across multiple host species. Vaccine strain shedding in milk occurred in 1.8–6.1% of vaccinated cows and buffaloes (culture-confirmed median 4.0%). Diagnostic interference (atypical seropositivity on smooth-LPS tests) was observed under field conditions, particularly after revaccination. Efficacy limitations included failure to protect against B. melitensis, B. suis, and B. ovis, waning immunity (< 4 years), and no benefit from revaccination. Human health risks included occupational accidental exposures (USA, Brazil, Egypt) and raw milk-associated RB51 infections (USA), complicated by intrinsic rifampin resistance.

Conclusions

RB51 preserves DIVA capability and induces cell-mediated immunity under ideal conditions but carries significant risks, including vaccine-induced abortion, milk shedding, and incomplete cross-protection. Its safety and effectiveness are highly context-dependent, performing well in low-prevalence countries with robust test-and-slaughter programs but failing in high-endemicity settings where pregnant adults are routinely vaccinated. Strict contraindication of RB51 in pregnant animals, pasteurization of dairy products from vaccinated herds, and complementary use of species-specific diagnostic tests are urgently needed. RB51 should not be used as a stand-alone intervention, and its continued use in endemic regions with mixed Brucella species requires re-evaluation.