Evaluation of the vaccine candidate ASFV-MEC-01: safety, efficacy, transmission dynamics, and assessment of reversion to virulence.

African swine fever (ASF) is a highly contagious and often fatal disease that poses a serious threat to global pig farming and food security. Despite decades of research, a safe and effective vaccine has not yet been widely implemented. In our previous study, we introduced ASFV-MEC-01, a novel live attenuated vaccine candidate developed through serial passaging of a field isolate in CA-CAS-01-A cells and subsequently characterized. In the present study, we further evaluated the safety parameters of ASFV-MEC-01. Specifically, we reaffirmed the safety and protective efficacy of ASFV-MEC-01 against a highly virulent Vietnamese ASFV strain. Notably, safety assessments were also conducted in pregnant sows. Furthermore, ASFV-MEC-01 showed no evidence of horizontal transmission to sentinel pigs and did not revert to virulence after consecutive in vivo passages, confirming its phenotypic stability. The vaccine also induced a sustained immune response in vaccinated pigs. Collectively, these findings demonstrate that ASFV-MEC-01 is a promising and safe live attenuated vaccine candidate, offering a valuable tool for effective ASF control.