The strains of JE vaccine were produced from Nakayama strain: S461, S462, S463 and from Beijing-1 strain: BS0704, BS0804, BS0904. The content of formalin for inactivation was 0.06% at 40C. The schedule for testing: 0, 3, 7, 14, 21, 28 and 35 days. The crude virus was inoculated directly into IC 0.03 ml/mouse then followed up within 14 days. Calculated LD50 according to Reed and Muench method. Results: LD50 decreased step by step and LD50 = 0 at the 28th days. That means from 28th days, crude vaccine which was produced from Nakayama and Beijing-1 strains were completely inactivated.
Encephalitis, Japanese ; Time Factors