Live vaccine preserved at room temperature: Preparation and characterization of a freeze-dried classical swine fever virus vaccine

The heat-stable live-attenuated classical swine fever virus (CSFV) vaccine is an urgent need in many countries of Asia, Europe and Latin America. In this study, the thermostability of lyophilized live-attenuated CSFV vaccine formulations were investigated using accelerated stability at 37 °C for 10 days. The freeze-dried heat-stable formulation ST16, containing excipient combinations of trehalose, glycine, thiourea and phosphate buffer shows the superior thermostability. Moreover, the lyophilized vaccine with formula ST16 kept loss of viral activity less than 0.5 log₁₀ during 24 months at storage temperatures of 2-8 °C. In thermal study, ST16 stabilized the vaccine within 1.0 log₁₀ loss after storage at up to 25 °C for 6 months and room temperature for 7 months. Even under the harshest storage conditions of 37 °C for 25 days and 45 °C for 2 weeks, the virus titer dropped less than 1.0 log₁₀ using ST16. Besides, it is notable that ST16 excluded gelatin and exogenous proteins, which might cause allergic reactions, thus avoiding immune side effects. The vaccine formulated ST16 proved to be safe and effective when immunized to piglets in vivo. The characteristics of dried vaccines were analyzed by X-ray powder diffraction, residual water measurements, differential scanning calorimetry and it was found that vaccine antigen were preserved in an amorphous matrix with high glass transition temperature above 60 °C and low residual water content below 2%, which made the vaccine more stable during storage.