Mills Deborah J, Gyawali Narayan, Nammunige Nirupama A, Mills Christine, Devine Gregor J, Lau Colleen L, Furuya-Kanamori Luis
Dr Deb The Travel Doctor, Travel Medicine Alliance, Brisbane, Australia.
UQ Centre for Clinical Research, Faculty of Health, Medicine, and Behavioural Sciences, The University of Queensland, Herston, Australia.
J Travel Med. 2025 Mar 11;32(2). doi: 10.1093/jtm/taaf006.
Japanese encephalitis virus is a leading cause of viral encephalitis in Asia, with high case-fatality rate and morbidity. Although the live recombinant Japanese encephalitis chimeric vaccine (Imojev®) offers strong initial immunity, data on long-term efficacy beyond 5 years remain limited.
We conducted a cross-sectional study on adults vaccinated with Imojev® at a specialist travel clinic in Brisbane, Australia. Participants were stratified based on the time since vaccination: 2-5 years and >5 years. Neutralizing antibody titres were measured using the plaque reduction neutralization test (PRNT50), with titres ≥10 indicating seropositivity.
Of the 103 participants, 47 were vaccinated 2-5 years prior and 56 were vaccinated ≥5 years prior to enrolment. All participants vaccinated within 5 years remain seropositive, whilst 52 of 56 (92.9%) vaccinated ≥5 years ago were seropositive. Four participants (7.1%) were seronegative post-vaccination, with time since vaccination ranging from 5 to 9 years. These seronegative individuals were vaccinated a median of 9.2 years ago, compared to 5.1 years for seropositive participants (P-value = 0.037). Aside from time since vaccination, no other factors (e.g. age, sex) were associated with seronegativity.
Imojev® provides durable immunity, with seropositivity exceeding 90% up to 10 years post-vaccination. However, waning immunity in a small proportion of individuals suggests that booster doses may be beneficial for high-risk travellers vaccinated over 5 years ago.
日本脑炎病毒是亚洲病毒性脑炎的主要病因，病死率和发病率都很高。尽管重组日本脑炎嵌合活疫苗（Imojev®）能提供强大的初始免疫力，但关于5年以上长期疗效的数据仍然有限。
我们在澳大利亚布里斯班的一家专业旅行诊所对接种了Imojev®的成年人进行了一项横断面研究。参与者根据接种疫苗后的时间分层：2至5年和超过5年。使用蚀斑减少中和试验（PRNT50）测量中和抗体滴度，滴度≥10表明血清反应阳性。
在103名参与者中，47人在入组前2至5年接种了疫苗，56人在入组前5年以上接种了疫苗。所有在5年内接种疫苗的参与者仍为血清反应阳性，而在5年以上接种疫苗的56人中，有52人（92.9%）血清反应阳性。4名参与者（7.1%）接种疫苗后血清反应阴性，接种疫苗后的时间为5至9年。这些血清反应阴性的个体接种疫苗的中位时间为9.2年前，而血清反应阳性的参与者为5.1年（P值 = 0.037）。除了接种疫苗后的时间外，没有其他因素（如年龄、性别）与血清反应阴性有关。
Imojev®提供持久的免疫力，接种疫苗后10年内血清反应阳性率超过90%。然而，一小部分人免疫力下降表明，加强剂量可能对5年以上接种疫苗的高危旅行者有益。
