© International Society of Travel Medicine 2019. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com. Journal of Travel Medicine, 2019, 1–3 doi: 10.1093/jtm/taz037 Perspective Perspective Japanese encephalitis vaccine for travelers: risk-benefit reconsidered Bradley A. Connor, MD 1 , Davidson H. Hamer, MD 2 *, Phyllis Kozarsky, MD 3 , Elaine Jong, MD 4 , Scott B. Halstead, MD 5 , Jay Keystone, MD 6 , Maria D. Mileno, MD 7 , Richard Dawood, MD, DTM&H 8 , Bonnie Rogers, RN, DrPH 9 , and William B. Bunn MD, JD, MPH 10 1 Department of Medicine, Weill Cornell Medical College and the New York Center for Travel and Tropical Medicine, NY, USA, 2 Department of Global Health, Boston University School of Public Health, and Section of Infectious Diseases, Department of Medicine, Boston Medical Center, Boston, MA, USA, 3 Department of Medicine and Infectious Diseases, Emory University (Emerita), Atlanta, GA, and Time Solutions, Chesapeake, VA, USA, 4 Division of Allergy & Infectious Diseases, Department of Medicine, University of Washington School of Medicine, Seattle, WA, USA, 5 Department of Preventive Medicine and Biostatistics, Uniformed Services University of the Health Sciences, Bethesda, MD, USA, 6 Tropical Disease Unit, Division of Infectious Disease, Toronto General Hospital and University of Toronto, Toronto, Ontario, Canada, 7 Division of Infectious Diseases, Department of Medicine, Warren Alpert Medical School of Brown University, and Brown Medicine, Brown Physicians, Inc., The Miriam Hospital, Providence, RI, USA, 8 Fleet Street Clinic, London, UK, 9 North Carolina Occupational Safety and Health Education and Research Center, University of North Carolina Gillings School of Global Public Health, Chapel Hill, NC, USA, and 10 Division of Neurology, Department of Internal Medicine, Medical University of South Carolina, Charleston, SC, and Department of Preventive Medicine, Northwestern University, Chicago, IL, USA * To whom correspondence should be addressed. Email: dhamer@bu.edu Submitted 23 March 2019; Revised 2 May 2019; Editorial Decision 2 May 2019; Accepted 2 May 2019 A number of years ago, an article on the risk of Japanese encephalitis (JE) in travelers by Shlim and Solomon quoted a popular movie at the time, ‘Chicken Run’, describing in a jocular fashion the one in a million chance of the imprisoned chickens mounting a successful escape. Rather than be deterred by this low probability, one of the protagonist chickens instead exhibited hope saying, ‘Then there is still a chance!’. 1 While past estimates suggest that the risk for a traveler to Asia of contracting JE was one in a million, 2 today there remains a risk of exposure to the JE virus and symptomatic disease, and the incidence of JE may be on the rise throughout Asia. Consequently, it is imperative that travel medicine practitioners provide risk prevention and awareness advice to those travelers at greatest risk. What we have learned about JE since the publication of this article should change the minds of the travel medicine community, and should also serve as a lesson to the traveling public. Let’s start with the oft quoted figure of risk being <1 case per million travelers. 2 Is this for all travelers to Asia, all trav- elers to at-risk or endemic areas for JE or a calculation using some other numerator and denominator? Fact is, these data are >10 years old, travel to Asia has markedly increased and because underreporting of JE may occur, we do not know precisely how many individuals travel to JE virus endemic regions, nor do we know how many actually acquire JE virus infection during travel. Consequently, we cannot be certain that we have accurate numerator and denominator data. 3 In endemic areas of Asia, it has been estimated that ∼70 000 JE cases occur annually, despite implementation of vaccination programs in some of these endemic areas. 3 Thus, the 70 000 inci- dence likely underestimates the true risk of disease for the non- immune traveler as returning travelers with signs and symptoms compatible with JE may be misdiagnosed as suffering from other viral illnesses, even if severe, and therefore go largely unreported to public health authorities. A combination of low levels of clinical suspicion, especially in the face of a non-specific febrile illness, as well as infrequent use of reliable laboratory testing even if illness is suspected, makes the diagnosis difficult. Over 50 years ago in a seminal work on JE infections, Scott Halstead cited the risk of clinical disease occurrence as being 1 in 25 if a naïve host (a traveler) is bitten by an infected mosquito in an endemic area. 4 Though the epidemiology of infection is dynamic, this information should be considered in Downloaded from https://academic.oup.com/jtm/article/26/5/taz037/5487229 by guest on 14 June 2022