# Efficacy Evaluation of an E2 Subunit Vaccine Against Highly Virulent Classical Swine Fever Virus Strain

## TL;DR

This study evaluates a new E2 subunit vaccine that effectively protects pigs against a deadly swine disease with a single dose.

## Contribution

The study introduces a novel E2-CpG subunit vaccine that provides robust immunity with a single dose.

## Key findings

- The E2-CpG vaccine induced higher anti-E2 antibody titers than a commercial vaccine at double dosage.
- The vaccine provided 100% protection against clinical symptoms and pathological changes in pigs.
- Viral shedding and spleen viral load were undetectable in vaccinated pigs after challenge.

## Abstract

Background/Objectives: Classical swine fever (CSF) is listed by the World Organisation for Animal Health as a highly devastating and contagious pig disease, causing severe economic losses to the swine industry. In spite of the successful elimination of CSF in Taiwan, preparedness against potential reintroduction remains essential. The live attenuated vaccines have been effective in disease control, but are not capable of a viable strategy that differentiates infected from vaccinated animals (DIVA). Subunit vaccines are recognized for their safety and ability to induce protective immunity against infectious diseases. Methods: In this study, the recombinant CSF virus (CSFV) E2 proteins were formulated with a CpG motif as an adjuvant to produce the E2-CpG subunit vaccine. Its efficiency in specific-pathogen-free (SPF) pigs was compared with a commercially available E2 subunit vaccine (Bayovac® CSF-E2; Bayer Taiwan Co., Ltd., Taipei City, Taiwan). Results: Significantly higher titers of anti-E2 antibodies were induced in pigs immunized with a single dose of the E2-CpG vaccine, particularly the reduced E-0.5A formulation, than those immunized with a dose of the commercialized E2 subunit vaccine adjusted to double dosage. This designed subunit vaccine showed high efficacy in protection against clinical symptoms and significant pathological alterations in pigs after a highly virulent CSFV (genotype 1.1) challenge. Viral shedding was not detected in vaccinated pigs before completion of the challenge study, and the viral load in their spleens remained undetectable. Conclusions: These results could support the potential of the E2-CpG vaccine as a cost-effective, single-dose subunit vaccine capable of inducing robust CSFV-specific immunity and providing 100% protection against lethal CSFV challenges.