Q1 · MEDICINE
ArticleOA
Author: Li, Rongcheng  ; Ong, Kien Chai  ; Zhou, Zhenxin  ; Cui, Pingfang  ; Wang, Xuanyi  ; Mo, Zhaojun  ; Che, Yanchun  ; Cui, Wei  ; Li, Qihan  ; Wang, Junzhi  ; Jiang, Li  ; Feng, Min  ; Zhang, Ying  ; Wang, Jingjing  ; Xie, Zhongping  ; Pu, Jing  ; Shi, Haijing  ; Wang, Lichun  ; Liang, Zhenglun  ; Xia, Jielai  ; Liao, Yun  ; Wong, Kum Thong  ; Wang, Ling  ; Huang, Teng  ; Zhao, Hongling  ; Guo, Lei  ; David, Perera  ; Liu, Longding  ; Tan, Soon Hao  ; Yang, Erxia  ; Dong, Chenghong  ; Mao, Qunying  ; Liang, Yan  ; Na, Ruixiong 
BACKGROUND:To investigate the long-term effects on immunity of an inactivated enterovirus 71 (EV71) vaccine and its protective efficacy.
 METHODS:A sub-cohort of 1,100 volunteers from Guangxi Province in China was eligible for enrolment and randomly administered either the EV71 vaccine or a placebo on days 0 and 28 in a phase III clinical trial and then observed for the following 2 years with approval by an independent ethics committee of Guangxi Zhuang Autonomous Region, China. Serum samples from the 350 participants who provided a full series of blood samples (at all the sampling points) within the 2-year period were collected. Vaccine-induced immune effects, including the neutralizing antibody titres and cross-protection against different genotypes of EV71, were examined. This study also evaluated the protective efficacy of this vaccine based upon clinical diagnosis.
 RESULTS:This sub-cohort showed a >60% drop-out rate over 2 years. The seroconversion rates among the 161 immunized subjects remained >95% at the end of study. The geometric mean titres of neutralizing antibodies (anti-genotype C4) 360 days after vaccination in 350 subjects were 81.0 (subjects aged 6-11 months), 98.4 (12-23 months), 95.0 (24-35 months), and 81.8 (36-71 months). These titres subsequently increased to 423.1, 659.0, 545.0, and 321.9, respectively, at 540 days post-immunization (d.p.i.), and similar levels were maintained at 720 d.p.i. Higher IFN-γ/IL-4-specific responses to the C4 genotype of EV71 and cross-neutralization reactivity against major EV71 genotype strains were observed in the vaccine group compared to those in the placebo group. Five EV71-infected subjects were observed in the placebo-treated control group and none in the vaccine-immunized group in per-protocol analysis.
 CONCLUSION:These results are consistent with the induction of dynamic immune responses and protective efficacy of the vaccine against most circulating EV71 strains.
 TRIAL REGISTRATION NUMBER:Clinicaltrials.gov, NCT01569581, Trial registration date: March 2012.