A comprehensive analysis of the current strategy for developing live attenuated vaccines against African swine fever: A systematic review and meta-analysis

A systematic review and meta-analysis were conducted to evaluate the safety and effectiveness of live attenuated vaccines (LAVs) against African swine fever (ASF) in domestic pigs, focusing on three major disease outcomes: mortality, fever, and clinical signs. The findings indicated that vaccinated pigs exhibited significantly lower risks of mortality (RR = 0.30, 95 % CI: 0.24-0.39), fever (RR = 0.46, 95 % CI: 0.38-0.56), and clinical signs (RR = 0.34, 95 % CI: 0.27-0.43), compared to unvaccinated controls, corresponding to vaccine efficacies (VE) of 70 %, 54 %, and 66 %, respectively. Although this marks significant progress toward ASF control through vaccination, the presence of significant side effects in some vaccinated pigs, such as fever (RD = 0.24, 95 % CI: 0.15-0.34) and clinical reactions (RD = 0.11, 95 % CI: 0.05-0.18) indicates that current vaccine candidates require further refinement to achieve the level of safety and protection needed for field application. Subgroup analysis revealed that homologous recombination technology is the most effective attenuation strategy, with gene deletion mutants derived from virulent strains achieving a VE of 73 % against mortality, 70 % against clinical signs, and 55 % against fever. Moreover, the efficacy and safety of LAVs are strongly influenced by the viral strain used as the vaccine backbone and the challenge strain used. A more comprehensive understanding of the antigenic, pathogenic, and immunogenic variations among ASF virus strains is crucial for the development of an effective and safe vaccine.