The deletion of the EP402R and MGF505/360 genes attenuates a genotype I/II recombinant ASFV but fails to confer complete protection against homologous or genotype II challenge in pigs

African swine fever (ASF), a pig disease caused by ASFV, is highly contagious and often lethal. The recent emergence of novel ASFV with I/II genomic recombination has posed significant challenges to global ASF prevention and control. In this study, we used the Chinese I/II genomic recombinant virulent strain ASFV-HN10005 (ASFV-HN) to construct two gene-deleted viruses. ASFV-HNΔMGF lacks the <i>MGF505-1R</i>-<i>MGF360-14L</i> genes cluster (including <i>MGF505-1R, -2R, -3R</i>, and <i>MGF360-12L, -13L, -14L</i>), and ASFV-HNΔCD2vΔMGF lacks both <i>EP402R</i> and the <i>MGF505-1R</i>-<i>MGF360-14L</i> genes cluster. ASFV-HNΔMGF still showed pathogenicity in domestic pigs, while ASFV-HNΔCD2vΔMGF showed markedly attenuated virulence, with all inoculated pigs surviving. However, these pigs did not gain complete protection against subsequent lethal challenge from the parental ASFV-HN strain or the virulent II-type strain ASFV-GZ. This implies that I/II genomic recombinant ASFV may have unique biological traits and immune evasion mechanisms. Our findings indicate the need to reassess current ASFV control strategies and provide a basis for future vaccine target selection.