Effects of binary ethyleneimine and formaldehyde inactivation methods on foot-and-mouth disease virus vaccine immune responses and kinetics.

Foot-and-mouth disease (FMD) is a highly contagious viral disease of livestock that has a significant economic impact on the country. The inactivated vaccine is the most widely used type of FMD vaccine, with the inactivation procedure being one of the most crucial steps. This study aims to evaluate the inactivation kinetics and post-vaccination immune responses of FMD vaccine developed using three inactivation methods: binary ethyleneimine (BEI), formaldehyde, and a combined approach. A randomized controlled trial included 20 healthy, unvaccinated calves, allocating five calves to each of the three vaccinated groups and one control (unvaccinated) group. A monovalent inactivated FMDV vaccine (O-ETH/38/2005) was developed using the above three inactivation methods. Each prepared vaccine was then randomly administered to seronegative experimental calves. Blood samples were collected at 0, 7, 14, 21, 28, and 42 days post-vaccination and analyzed using solid-phase competitive enzyme-linked immunosorbent assay to assess the antibody response level. Regression analysis demonstrated that both the combined and BEI-inactivated vaccines exhibited linear kinetics, with higher and comparable virus titer reduction rates of 1.27 and 1.05 log10 TCID50 per hour, respectively. The formaldehyde-inactivated vaccine exhibited curvilinear kinetics with a slower rate of 0.34 log10 TCID50 per hour. This demonstrated that methods for virus inactivation lead to significant variability in the antibody responses induced by the vaccine. Significantly higher antibody titer (p = 0.006) was found in a vaccine inactivated by combined methods compared to those inactivated using formaldehyde. Comparative analysis revealed no significant difference in antibody responses between combination-inactivated and BEI-inactivated vaccines (p = 0.696). This study revealed that the combined approach has faster inactivation and better immune induction. Thus, It is recommended to replace formalin with a combined inactivant following optimization and validation of strain-specific inactivation procedures to enhance FMD vaccine efficiency.