What risk do Brucella vaccines pose to humans? A systematic review of the scientific literature on occupational exposure.

IntroductionVaccination of cattle, sheep and goats with attenuated strains of Brucella is an effective measure for controlling brucellosis, although the vaccines pose risks to humans during the manufacturing process and throughout their distribution and administration to animals. ObjectiveThe aim of this study was to review the risk posed to humans by occupational exposure to vaccine strains and the measures that should be implemented to minimize this risk. Materials and methodsThis article reviewed the scientific literature indexed in PubMed up to January 31, 2023, following "the PRISMA guidelines"; special emphasis was placed on the vaccine strain used and the route of exposure. ResultsTwelve primary reports were found: six included the Rev-1 strain, three the S19, and four the RB-51 strain. Rev-1 seemed to be the most virulent. The most frequent type of exposure was needle injury during administration, while exposure accidents during vaccine manufacturing were exceptional. Prolonged contact with the pathogen, lack of information and a low adherence to personal protective equipment (PPE) use in the work environment were determining factors for becoming infected. Despite strict protection measures, a percentage of vaccine manufacturing workers developed a positive serology to the vaccine strain, which may have conferred immunity. ConclusionsBrucella vaccines pose risk of contagion to humans from their production to their administration to cattle; therefore, protection measures should be extreme, and active surveillance of exposed workers should be implemented.