Japanese encephalitis: defining risk incidence for travelers to endemic countries and vaccine prescribing from the UK and Switzerland

BACKGROUND: Large numbers of Western travelers visit countries endemic for Japanese encephalitis (JE). The risk of infection is unknown. This study attempts at estimating a risk incidence for visitors from two European countries with the available data. METHODS: Using the total number of case reports between 1978 and 2008, the number of visits made by European tourists to endemic regions, and total doses of vaccines sold in the two study countries, the risk incidence of JE in travelers was estimated. The proportion of vaccinated visitors to endemic regions was retrieved from the data of two travel clinics (in London and Basel) and related to vaccine prescribing in UK and Swiss travelers. RESULTS: In 2004, an estimated 0.16% to 0.3% of UK and Swiss travelers were vaccinated against JE, with no surveillance reports of JE cases. Between 116,000 and 152,000 European travelers would receive vaccination. More than 99% travel to endemic countries without vaccination. Only 40 cases of JE infection have been reported in travelers for the past 30 years. The risk incidence is thus 1.3 per year in 7.1 million visits of the 17 million European travelers who are at a potential risk of JE infection. CONCLUSIONS: This study and the analysis of the existing literature support the recommendation that all travelers should be informed about the risk of JE infection but also suggest that there is no evidence for justifying a general recommendation for JE vaccination in travelers to endemic areas.