ENHANCEMENT OF THE THERMOSTABILITY OF FOOT AND MOUTH DISEASE OIL VACCINE USING CALCIUM CHLORIDE

Improving the thermostability of foot-and-mouth disease (FMD) vaccines is essential for maintaining potency, particularly during vaccination campaigns, where cold chain maintenance may be challenging. This study investigates the potential of calcium chloride (CaCl2) as a stabilizing agent to enhance the stability and efficacy of FMD vaccines under varying storage temperatures. Monovalent vaccines against FMD serotype SAT2, with and without CaCl2, were formulated and evaluated for safety, immunogenicity, and stability. Calves vaccinated with the CaCl2-treated vaccine exhibited antibody titers, kinetics, and duration comparable to the untreated group, indicating no adverse impact on the immune response. Vaccine samples were stored at 4°C, 25°C, and 37°C for up to five weeks. Stability was assessed by measuring 146S particle content, and potency was evaluated weekly by protection tests in guinea pigs following homologous virus challenge. At 4°C, both formulations maintained stability. At 25°C, the treated vaccine retained 0.6 µg/dose of 146S particles after five weeks, whereas the untreated retained only 0.3 µg. Correspondingly, protection rates were higher for the treated vaccine (60% vs. 40% after two weeks of storage). At 37°C, the treated vaccine showed improved 146S particle retention for one additional week and provided better protection in guinea pigs after the first week of storage, although both formulations declined rapidly thereafter. These findings suggest that CaCl2 enhances the thermal stability of FMD vaccines at higher temperatures. While this additive demonstrates promise for improving vaccine thermostability, maintaining the cold chain remains critical to ensure field effectiveness.