Establishment of the safety of African swine fever attenuated live vaccines: The role of viremia and post-market surveillance systems

African Swine Fever (ASF) live-attenuated vaccines (LAVs) present multiple safety concerns, including virulence reversion, recombination, persistent viremia, and reproductive safety in gestating sows. The Vietnam's commercialization experience high light the need to re-evaluate the safety of gene-deleted LAVs. The magnitude and duration of viremia are key indicators of vaccine safety. Cases of fetal abnormalities, transplacental transmission, and virulence reversion following vaccination of pregnant sows underscore the limitations of clinical trials and the long-term, multi-generational risks associated with vaccine use. Accordingly, broad regulatory standards are required, covering safety in piglets and sows, horizontal transmission, virulence reversion, and environmental risks from living modified organisms (LMOs). The establishment of a molecular epidemiology-based post-marketing surveillance (PMS) system is needed. This system should include pre-introduction characterization of regional circulating strains, post-vaccination active surveillance, and whole-genome sequencing to monitor for mutations. A regulatory-scientific framework ensuring both safety and efficacy must be established through international collaboration and standardized reporting systems.