Assessment of the reversion to virulence and protective efficacy in pigs receiving the live attenuated classical swine fever recombinant vaccine candidate FlagT4G

Authors: Ramirez Medina, Elizabeth; Velazquez Salinas, Lauro; VALLADARES, ALYSSA - Oak Ridge Institute For Science And Education (ORISE); RAI, AYUSHI - Oak Ridge Institute For Science And Education (ORISE); Hall, Leeanna; Sastre, Leandro; Silva, Ediane; GANGES, LLILIANNE - Research Center For Animal Health; Gladue, Douglas; Borca, Manuel

Submitted to: Vaccines
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2025
Publication Date: 5/20/2025
Citation: Ramirez Medina, E., Velazquez Salinas, L., Valladares, A., Rai, A., Burton, L.J., Sastre, L.P., Silva, E.B., Ganges, L., Gladue, D.P., Borca, M.V. 2025. Assessment of the reversion to virulence and protective efficacy in pigs receiving the live attenuated classical swine fever recombinant vaccine candidate FlagT4G. Vaccines. 13(5). Article 544. https://doi.org/10.3390/vaccines13050544.
DOI: https://doi.org/10.3390/vaccines13050544

Interpretive Summary: The manuscript describes the safety and efficacy of the vaccine strain called FlagT4G to protect pigs from the disease caused by classical swine fever virus (CSFV). CSFV causes an transmissible lethal disease (CSF) that affect pigs of all ages. The manuscript demonstrates that FlagT4G is very safe and is affective to protect pigs against CSF.

Technical Abstract: Control of classical swine fever virus (CSFV) in endemic countries relies on vaccination using live attenuated vaccines (LAV). Most of these LAV do not allow for the differentiation of vaccinated animals from infected animals (DIVA) based in their serological response. FlagT4G vaccine is a novel candidate that confers robust protective immunity early after vaccination and shows DIVA capabilities. This report presents the characterization of FlagT4G virus in terms of the stability of its genomic and attenuated phenotype assessed by a reversion to virulence protocol, as well as its protective efficacy by determining the minimal protective dose. Results presented here demonstrate that after five consecutive passages in groups of 5-week-old susceptible domestic pigs, FlagT4G virus remains genetically stable, and its attenuated phenotype remained unaltered. In terms of efficacy, FlagT4G virus induced solid protection against the intranasal challenge with 105 tissue culture infectious dose (TCID50) of virulent field isolate Brescia virus even with a vaccine dose as low as 102 TCID50. Results presented here indicate that FlagT4G vaccine may be a useful tool for CSFV control.