Stability of Freeze-dried Inactivated Japanese Encephalitis Vaccine under Different Experimental Conditions

Abstract

Stability of three batches of freeze dried inactivated mouse brain Japanese encephalitis vaccine, was evaluated in terms of percentage drop or otherwise in potency from their respective initial titers, after exposure to different experimental conditions for 4 -12 weeks. The potency was assayed by plaque reduction neutralization assay (PRNT) using chick embryo fibroblasts cells. The vaccine has been found to be stable i.e. retain potency (mean drop 3.99%) till 12 weeks when exposed at 25 0 C ± 2 0 C and 80-90% relative humidity (RH). At 37 0 C ± 1 0 C and when kept in vertical position, the vaccine showed an average drop of 10.42% in potency after 12 weeks, while it was 11.0% and 10.42% in horizontal positions and inverted position respectively. Exposure at higher temperature (45 0 C + 1 0 C and 80-90% RH) led to deterioration of potency (25.82%) after 8 weeks. A maximum average drop of 7.66% in potency was observed when vaccine was exposed to sunlight compared to 4.29% in case of artificial light after 12 weeks indicating that the JE vaccine should not be exposed to direct light. Thus, even if this vaccine gets exposed to higher temperature for a short duration, it appears that FD JE vaccine may be potent enough for effective seroconversion in the field.