Studies on Japanese B encephalitis virus vaccines from tissue culture. VI. Development of a hamster kidney tissue culture inactivated vaccine for man. (1). Obtaining maximum titers of virus using an attenuated strain of OCT-541.

Summary The growth curve of the OCT-attenuated 35-24°C line of JBE virus in HKC culture and factors resulting in increase of the virus yield were investigated for the purpose of vaccine production. Comparing 199, Eagle9s basal, and Leibovitz media with the addition of 2% H.Al. there was no advantage of one over the other in respect to the titer of the virus yield. In medium 199 containing 2% H.Al. of pH 7.0, the titer of the complete harvest was always more than 1.0 log higher than that of the fluid harvest. When a medium of pH 8.0 was used, the titer of the fluid harvest was comparable to or slightly higher than that of the complete harvest at pH 7.0 and almost equal to that of complete harvest at pH 8.0. In medium 199 containing H.Al., a direct correlation between infectivity and hemagglutinin was noticed. Within the range tested, reduction of the amount of medium employed for the final harvest resulted in a proportional increase in yield of virus. It appears that titers of infectivity between 10 9 and 10 10 per ml and of HA between 1:256 and 1:512 can be readily obtained without any concentration procedures and with no foreign protein present except that of the disintegrated tissue cells used as a substrate.