Evaluation of the Safety Profile of the ASFV Vaccine Candidate ASFV-G-ΔI177L.

African swine fever (ASF) is the cause of a recent pandemic that is posing a threat to much of the world swine production. The etiological agent, ASF virus (ASFV), infects domestic and wild swine, producing a variety of clinical presentations depending on the virus strain and the genetic background of the pigs infected. No commercial vaccine is currently available, although recombinant live attenuated vaccine candidates have been shown to be efficacious. In addition to determining efficacy, it is paramount to evaluate the safety profile of a live attenuated vaccine. The presence of residual virulence and the possibility of reversion to virulence are two of the concerns that must be evaluated in the development of live attenuated vaccines. Here we evaluate the safety profile of an efficacious live attenuated vaccine candidate, ASFV-G-ΔI177L. Results from safety studies showed that ASFV-G-ΔI177L remains genetically stable and phenotypically attenuated during a five-passage reversion to virulence study in domestic swine. In addition, large-scale experiments to detect virus shedding and transmission confirmed that even under varying conditions, ASFV-G-ΔI177L is a safe live attenuated vaccine.

African swine fever virus vaccine candidate ASFV-G-ΔI177L efficiently protects European and native pig breeds against circulating Vietnamese field strain.

The recent spread of African swine fever (ASF) in the People's Republic of China and neighbouring countries in Asia has had significant economic consequences with an estimated direct cost of $55-$130 billion. This pandemic, originally detected in Republic of Georgia in 2007, has devastated the swine industry in large geographical areas of Southeast Asia with 14 countries reporting ASF outbreaks since the first documented case was confirmed in the city of Shenyang, Liaoning Province, China, on 3 August 2018. In the absence of any available vaccines, the control of ASF relies on the detection and culling of infected animals. The United States Department of Agriculture recently developed a recombinant experimental vaccine candidate, ASFV-G-ΔI177L, by deleting the I177L gene from the genome of the highly virulent pandemic ASFV strain Georgia, which efficaciouly protects pigs from the parental virus. Here, the initial studies were extended demonstrating that ASFV-G-ΔI177L is able to protect pigs against the virulent ASFV isolate currently circulating and producing disease in Vietnam with similar efficacy as reported against the Georgia strain. Comparative studies performed using a large number of pigs of European and Vietnamese origin demonstrated that a minimum protective dose of 102 HAD50 of ASFV-G-ΔI177L equally protects animals of both breeds. In concurrence with those results, the onset of immunity in these animal breed showed appearance of protection in approximately one-third of the animals by the second week post vaccination, with full protection achieved by the fourth week post vaccination. Therefore, results presented here demonstrated that ASFV-G-ΔI177L is able to induce protection against virulent Vietnameese ASFV field strains and is effective in protecting local breeds of pigs as efficiently as previously shown for European cross-bred pigs. To our knowledge, this is the first report showing the efficacy of a Georgia 2007 based vaccine candidate in Asian breed of pigs or challenged with an Asian ASFV strain.