Comparative Efficacy of Stabilizers on the Thermostability of Peste des Petits Ruminants Vaccine

Peste des petits ruminants (PPR) is an acute and highly contagious fatal disease of small ruminants mainly affecting sheep and goats, and camels. PPR is endemic disease in many developing and tropical countries including Pakistan, and vaccine is currently the only means of disease control. However, lack of established infrastructures and high temperature, maintaining cold chain for effective delivery of the vaccine is a challenge. All vaccines that are currently being applied for the control of PPR are thermo-labile and require cold chain for stability. In this study, we assessed the efficacy of different stabilizers on the thermostability of live attenuated vaccine of PPR virus (PPRV). Five formulations of four thermo stabilizers including lactalbuminhydrolysate sucrose (LS), trehalose dihydrate (TD), weybridge medium (WBM) and buffered gelatin sorbitol (BUGS) were used to prepare vaccine using Nigeria 75/1 strain of PPR virus. Results revealed that vaccine having LS proved maximum stability as it reduced minimal viral infectivity (0.42 log10TCID50) during lyophilization as well as three time higher shelf life (3.69 days) as compared to commercial vaccine (1.23 days) at 37°C. Moreover, it was also revealed that PPR vaccine lyophilized with LS, WBM and TD, and was more stable than commercial vaccine having shelf life of 206-304 days at 4°C, 8-10 days at 25°C and 2.5-3.7 days at 37°C. Using regression analysis on the shelf life of vaccine preparations in different thermo stabilizers, we can demonstrate that BUGS provided minimal stability as well as maximum viral infectivity loss (1.49 log10TCID50) after lyophilization. Taken together, we provide foundation studies to improve the thermostability of PPRV to facilitate the immunization of susceptible animals in situations where meeting cold chain is not feasible. Efforts are required to genetically select strains that confer protection at higher temperature without compromised immunogenicity which is potentially feasible with the established reverse genetics.