Studies on Japanese B Encephalitis Virus Vaccines from Tissue Culture

Abstract

Summary The virulent OCT-541 strain of Japanese B encephalitis (JBE) virus grown in hamster kidney cell (HKC) monolayers and harvested in medium 199 containing 2% human albumin (H. Al.) at pH 7.1 was inactivated by heat and 1:4000 formalin at 30° and 37°C. The half-life of the virus was 14 and 5 hr at the two temperatures, respectively. The formalin inactivation curves at both temperatures were biphasic with the change in rate of inactivation occurring early in the reaction, within 2 hr. The reaction based on two trials appeared to proceed at a faster rate when carried out at pH 8.0 than at pH 7.0. The inactivation preparation when tested for potency by the mouse test gave a low, mean MID of 0.0033 ml (very high potency). The virulent OCT-541 was similar to the OCT-541 attenuated strain in thermal stability and in the nature of the formalin inactivation curves. Nevertheless the potency of the wild strain was always two to three times better than that of the attenuated strain by the mouse MID test. When two inactivated lots of vaccine prepared simultaneously from the two strains were tested for potency, the potency of the wild strain was confirmed by the mouse test as 2.8 times better, and shown by the guinea pig antigen extinction test as 1.6 times better. The relative merits of the wild strain and the attenuated one for vaccine manufacture and use were discussed.