目的 观察肠道病毒71型（enterovirus 71，EV71）疫苗III期临床试验接种5年的免疫持久性。方法 在III期临床试验免疫原性亚组中，对完成全程两针次免疫的免前抗EV71中和抗体阴性人群进行免疫后5年采血并检测抗EV71中和抗体，对0 d、56 d、8个月、14个月、26个月、64个月同时具有抗EV71中和抗体检测数据人群评价免疫持久性。结果 共614名受试者完成5年免疫持久性血样采集并获得中和抗体检测结果，其中490名受试者同时具有0天、56 d、8个月、14个月、26个月、64个月抗EV71中和抗体检测数据，疫苗组和安慰剂对照组分别为235名和255名。EV71疫苗免疫后5年，疫苗组抗EV71中和抗体阳性率（100.00%）和抗体几何平均滴度（geometric mean titer，GMT）（369.57）均高于对照组（69.02%和55.58）。分别以抗体滴度8、16、32为阳性判定标准，疫苗组阳性率（100%、99.57%、97.87%）均高于对照组（69.02%、61.96%、59.61%）。对不同年龄亚组进行分析，6~11、12~35月龄受试者免疫后疫苗组5年抗EV71中和抗体阳性（滴度≥8）率（均为100.00%）和抗体GMT（367.14、370.64）均高于对照组（66.67%、71.27%和53.43、63.66）。在EV71疫苗免疫后的各个时间点，疫苗组抗EV71中和抗体阳性率和GMT均高于对照组。结论 该EV71疫苗两针基础免疫后能够诱导良好的免疫原性，在免疫后5年依然保持较好的免疫持久性。

 Objective  To investigate the immunity persistence five-year following two-dose vaccination of inactivated enterovirus 71 (EV71) vaccine. Methods  For EV71 neutralizing antibody (NAb) testing, blood samples were collected from a subset of participants whose serum NAb assay was negative on day 0 in the immunogenicity cohort fulfilled the two doses vaccination protocol. The full series of sampling points included day 0, day 56, month 8, month 14, month 26, and month 64. Results  614 subjects completed blood sample collection and obtained NAb results. Combined with the previous observation, 490 subjects had the full series of sampling points including day 0, day 56, month 8, month 14, and month 64; with 235 vaccine subjects and 255 placebo subjects. 5 years after vaccination, the positive rates and the geometric mean titers (GMTs) of anti-EV71 NAb in vaccine group (100.00% and 369.57) were higher than those in placebo group (69.02% and 55.58). By the cutoff NAb titer values of 8, 16, 32, 5 years post the 1st vaccination, the seropositive rates in vaccine group (100.00%, 99.57%, 97.87%) were higher than those in placebo group (69.02%, 61.96%, 59.61%). In both 6-11 and 12-35 month subgroups, in vaccine group, 5 years post the 1st vaccination, the NAb seropositive (titer≥8) rates (both 100.00%) and GMTs (367.14, 370.64) were higher than those in placebo group (66.67%, 71.27%, and 63.66, 53.43). At all observed time points, the seropositive rates and GMTs in vaccine group were higher than that of placebo group. Conclusion  The EV71 vaccine induces a sustained high level of NAb GMTs and seropositive rates against EV71 for at least 5 years in healthy Chinese children.