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The article discusses the vaccination of travelers against Japanese encephalitis. The recommendations for Japanese encephalitis has been for high-risk circumstances but due to serious and fatal cases of Japanese encephalitis there has been a call for broader vaccine coverage. The vaccine against Japanese encephalitis was developed from a highly reactogenic mouse brain though there is another inactivated cell culture-derived vaccine. Vaccination against Japanese encephalitis should be recommended for repeat and long-term travelers to endemic areas of Asia.

Background: Japanese Encephalitis (JE) virus occurs in wide regions of Asia with over 3 billion people living in areas at risk for JE. An estimated 68,000 clinical cases of JE occur every year, and vaccination is the most effective prophylactic measure. One internationally licensed vaccine containing the inactivated JE virus strain SA14-14-2 is Ixiaro (Valneva, Austria). According to recommendations, basic immunization consists of vaccinations on day 0, day 28, and a booster dose 12-24 months later. Protection in terms of neutralizing antibody titers has been assessed up to 12 months after the third dose of the vaccine. The current investigation was designed to evaluate antibody decline over time and to predict long-term duration of seroprotection after a booster dose., Method: In a preceding trial, volunteers received basic immunization (day 0, day 28) and one booster dose against JE 15 months later. A follow up blood draw 6 years following their booster dose was carried out in 67 subjects. For antibody testing, a 50% plaque reduction neutralization test (PRNT50-test) was used. PRNT50 values of 10 and above are surrogate levels of protection according to WHO standards., Result: Seventy-six months following the booster dose, 96% of the tested subjects had PRNT50 titers of 10 or higher. Geometric mean titer (GMT) was 148 (95% CI confidence interval: 107-207). Antibody titers were lower in volunteers 50 years of age and older. Vaccination history against other flaviviruses (yellow fever or tick borne encephalitis) did not significantly influence PRNT50 titers. A two-step log-linear decline model predicted protection against JE of approximately 14 years after the booster dose., Conclusion: Six years after a booster dose against JE, long-term protection could be demonstrated. According to our results, further booster doses should be scheduled 10 years following the first booster dose., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The mosquito-borne Japanese encephalitis virus causes an estimated 50,000 cases in Asia, accounting for at least 10,000 deaths and 15,000 cases of neuropsychiatric sequelae. IXIARO (Intercell AG, Vienna, Austria), an inactivated, Vero cell-derived vaccine against Japanese encephalitis was introduced in 2009. The vaccine is highly immunogenic, showing significantly higher geometric mean antibody titers compared with previous, mouse brain-derived vaccines. Postmarketing studies have confirmed the excellent safety profile. Studies on children aged 2 months to 18 years have been published. Based on these data, positive opinion from the EMA for vaccination of children has recently been given. Since a safe and effective vaccine against Japanese encephalitis is now available, outdated guidelines and recommendations have to be revised: travelers to rural areas of Asia should generally be recommended vaccination.

The mosquito-borne Japanese encephalitis virus (JEV) is a major threat to human health in Asia. An estimated 50,000 cases occur in the region, accounting for at least 10,000 deaths and 15,000 cases of neuropsychiatric sequelae. A new purified, inactivated JEV vaccine (IC51, Ixiaro) has been developed. Since early 2009, the vaccine has been licensed in Australia, the USA and Europe. A series of successful Phase III studies has been published. Results indicate a very good safety and efficacy profile. The vaccine promises to become a modern approach to active immunization against Japanese encephalitis. With the availability of a new product, wider use of Japanese encephalitis vaccine will be prudent in the future, and guidelines and recommendations should be revised.