目的   观察乙型脑炎（乙脑）减毒活疫苗的接种反应和免疫原性。 方法   分别选择52名（8月龄～50岁）和607名（8月龄～12岁）健康志愿者进行Ⅰ和Ⅲ期临床试验。试验组每人接种1次由上海生物制品研究所有限责任公司研制的乙脑减毒活疫苗（0.5 ml），对照组接种同样剂量的已上市乙脑减毒活疫苗。两组接种后的不良反应率和中和抗体阳转率用χ²检验进行比较，中和抗体几何平均滴度用t检验进行比较。 结果   试验组接种后有5.91%的人体温升高，对照组为7.96%，两组的体温反应发生率差异无统计学意义（χ²=0.917，P=0.338）。试验组Ⅰ期试验局部反应率为1.92%，Ⅲ期试验为0.25%，对照组Ⅲ期试验局部反应率为0.50%，两组的局部反应率差异无统计学意义（确切概率法，P=0.553）。Ⅲ期免疫原性试验中，试验组的血清中和抗体阳转率为89.00%，抗体几何平均滴度为29.69；而对照组分别为74.59%和19.25，差异均有统计学意义（χ²=11.708，P=0.001；t=4.281，P=0.001）。 结论   本研究的试验性乙脑减毒活疫苗接种反应轻微，并具有良好的免疫原性。

 Objective   To observe adverse reaction and immunogenicity of an attenuated Japanese encephalitis live vaccine for human use.  Methods   PhasesⅠand Ⅲ clinical trials were performed in 52 healthy volunteers aged betwween 8 months to 50 years and 607 children aged betwween 8 months to12 years, respectively. Subjects were inoculated with 1 dose (0.5 ml) of the test vaccine. A licensed vaccine was used as control. The rates of adverse reaction and seroconversion between the test and control groups were compared with chi-square test. Geometric mean titer (GMT) of neutralizing antibody was compared with t-test between the two groups.  Results  The rates of rise in temperature were 5.91% and 7.96% in the test group and control group, respectively. There was no statistical difference between the two groups (χ²=0.917, P=0.338). The rates of local reaction in test group were 1.92% and 0.25% in PhasesⅠand Ⅲ, respectively, compared with 0.50% in control group in Phase Ⅲ. No significant difference was found between the two groups (exact probability, P=0.553). The seroconversion rates and GMT of neutralizing antibody in test group were 89.00% and 29.69, compared with 74.59% and 19.25 in control group (χ²=11.708, P=0.001; t=4.281, P=0.001).  Conclusion The test vaccine is proved to be safe and immunogenic.