Patient description: An 18-year-old male returning from a recent vacation in Asia presents to the ER with a sudden onset of high fever, chills, facial flushing, epistaxis and severe headache and joint pain. His complete blood count reveals leukopenia, increased hematocrit concentration and thrombocytopenia.

Clinical trial eligibility criteria: eligible ages (years): 18.0-48.0,  Japanese Encephalitis All aspects of the protocol explained and written informed consent obtained from the participant Aged ≥18 to < 49 years In good general health, without significant medical history, physical examination findings, or clinically significant abnormal laboratory results Participant must be available for the study duration, including all planned follow-up visits Participant must agree to take the following precautions to avoid insect bites for 7 days following vaccination by using N,N-diethyl-meta-toluamide (DEET)-containing insect repellent, where appropriate For female participants: Negative pregnancy tests at Screening and Day 0, in conjunction with a menstrual and contraceptive history indicating a low probability of pregnancy in the opinion of the physician. Females of childbearing potential will be required to be correctly using an efficacious hormonal method of contraception or intrauterine device for at least 1 month before randomisation and during the on-study phase to Day 30. Barrier methods of contraception will not be considered acceptable for study entry. Female participants of child-bearing potential will sign an agreement that contraception will be correctly practised during the specified periods and will specify the method used. Female participants unable to become pregnant must have this documented (e.g., tubal ligation, hysterectomy or postmenopausal [at least one year since last menstrual period])  A history of vaccination or infection to Japanese encephalitis (JE) or yellow fever (YF) or other flaviviruses (including Japanese encephalitis, tick-borne encephalitis, St Louis encephalitis, West Nile virus, dengue fever, Murray Valley encephalitis). Previous vaccination will be determined by history (interview of subject) Previous or current military service History of residence in or travel to flavivirus endemic areas in the tropics (Cape York region of Northern Queensland, India, Southeast Asia, Central America, Caribbean or South America) for periods of 4 weeks or more Known or suspected immunodeficiency (e.g., human immunodeficiency virus [HIV] infection, primary immunodeficiency disorder, leukemia, lymphoma), use of immunosuppressive or antineoplastic drugs (corticosteroids > 10 mg prednisone, or equivalent, in the last three months or during the trial (up to Day 30) History of thymoma, thymic surgery (removal) or myasthenia gravis Clinically significant abnormalities on laboratory assessment (i.e., meeting the mild, moderate or severe described in the toxicity gradings for laboratory values) Anaphylaxis or other serious adverse reactions characterised by urticaria or angioedema to foods, hymenoptera (bee family) stings, or drugs (including vaccines) Transfusion of blood or treatment with any blood product, including intramuscular or intravenous serum globulin within six months of the Screening Visit or up to Day 30 Administration of another vaccine or antiviral within 30 days preceding the screening visit or up to Day 30 (these subjects will be rescheduled for vaccination at a later date) Physical examination indicating any clinically significant medical condition