Safety of Live Attenuated ASFV‐G‐ΔI177L/ΔLVR Vaccination in Sows With Advanced Pregnancies

African swine fever (ASF) causes severe disease in domestic pigs and wild boars and often results in 100% mortality. The use of attenuated strains in ASF vaccine development, based on the most recently studied ASF virus (ASFV)-Georgia (ASFV-G) strain, has proven effective. In July 2023, Vietnam became the first country in the world to have two indigenously developed ASF vaccines approved for commercial sale locally. In this study, we evaluated the immunogenicity and safety of the live attenuated vaccine (LAV) ASFV-G-ΔI177L/ΔLVR derived from ASFV-G-ΔI177L in five pregnant sows and a control group. The ASFV-G-ΔI177L replicates efficiently in a stable swine cell line. Therefore, the pregnant sows were used to validate the vaccine. Fundamental assessments of clinical symptoms (vaccine safety), parturition performance, vertical transmission presence after birth, and maternal antibodies were conducted before and after colostrum intake following the vaccination with ASF-G-ΔI177L/ΔLVR. The vaccination had no adverse effects and induced a high level of antibody production. Normal delivery was also confirmed without miscarriages. Furthermore, ASF antibodies and the P72 gene were detected in the blood of most piglets that consumed colostrum from vaccinated sows, and transplacental transmission was confirmed in piglets following vaccination. While these results will influence vaccine development and play an important role in preventing lethal ASFV infections, they also highlight the potential of ASFV-G-ΔI177L/ΔLVR to protect even high-risk groups such as pregnant sows and emphasize the importance of continued vigilance and investigation of vaccine safety parameters such as viral shedding, genetic stability, and reproductive efficacy.