Safety and genetic stability of African swine fever virus vaccine candidate “ASFV-G-∆MGF” in an in vivo “reversion to virulence” study : [Preprint]

African swine fever (ASF) has gained panzootic dimensions and commercial vaccines are still unavailable. Recently, a series of live attenuated vaccines has raised hope for an efficacious and safe vaccine, among them “ASFV-G-∆MGF”. We tested the latter in a in vivo reversion to virulence study in accordance with International Cooperation on Harmonisation of Technical Requirements for Registration of Veterinary Medicinal Products guidelines. Upon forced animal passaging, a virus variant emerged that was associated with transient fever and an increased replication and shedding. However, all animals were healthy upon completion of the study and reversion to significant virulence was not observed. The genomic changes involved deletions and reorganizations in the terminal regions of the genome. While our study underscores that in-depth safety characterization is needed for live ASF vaccines, one should still conduct a thorough benefit risk analysis considering all safety and efficacy aspects when assessing their use in disease control.