African swine fever vaccine ASFV-G-ΔI177L induces solid protection in four-week-old piglets

African swine fever (ASF) is an important disease of swine currently affecting pig production worldwide. Vietnam is, currently, the only country where commercial live attenuated vaccines are being freely used in the field. One of these vaccines is based in the use of the ASFV-G-ΔI177L strain, a recombinant virus developed by a partial deletion in the I177L gene from the highly virulent parental strain Georgia 2010. The commercial version of the vaccine was originally limited to use in pigs between 8 and 10 weeks of age, which significantly restricts its use. In this report, we demonstrate that pigs can be vaccinated as early as the fourth week of age, producing an efficacious immune response that fully protects the animals against the challenge with the virulent Vietnamese field strain TTKN/ASFV/DN/2019 and thus increasing the vaccine's usage to pigs 4-10 weeks of age. Several groups of four-week-old pigs were intramuscularly (IM) vaccinated with a single dose of a commercial vaccine containing 10^2.6 HAD₅₀ of ASFV-G-ΔI177L and IM challenged 28 days later with 10² HAD₅₀ of TTKN/ASFV/DN/2019. All the vaccinated animals remained clinically normal after vaccination, demonstrating no presence of residual virulence of ASFV-G-ΔI177L in animals of this age. In addition, all vaccinated animals remained protected after the challenge, showing no clinical signs associated with ASF during the observational period. These results corroborate the safety and efficacy of the ASFV-G-ΔI177L vaccine strain when used in pigs as early as four week of age.