Epidemiology of tick-borne encephalitis (TBE) in international travellers to Western/Central Europe and conclusions on vaccination recommendations

Abstract

Background: Tick-borne encephalitis (TBE) endemicity is spreading in Europe becoming an increasing health risk also for travellers. Previous reviews on TBE in civilian travellers lacked of numerator data and offered at most rough estimates on denominator data. An evidence-based quantification of the risk so far has been impossible; that resulted in fundamentally differing vaccination recommendations. Methods: A standard internet search was conducted with a focus on the data used to formulate vaccination recommendations. As TBE became notifiable at the European Union (EU) level the databases of European Center for Disease Prevention and Control (ECDC) were analysed for cases imported from abroad 2012. Since these included only 19 EU countries, individual experts were contacted in countries, which had not submitted data and additional surveillance databases were investigated to obtain a comprehensive account on travel-associated TBE in Central and Western Europe. Results: In 2012, the ECDC and other data sources included 38 reported cases of internationally acquired TBE. Basing on estimates of the exposed number of visitors, the attack rate for an undefined period of time could be very roughly extrapolated to be 0.5-1.3 per 100 000 (1 per 77 000-200 000) overall in Western/Central Europe endemic areas for the exposed at-risk population. Conclusions: As advised by the World Health Organization (WHO) travellers exposed outdoors in rural endemic areas to a risk of TBE during the period of transmission should be recommended immunization. In contrast, the advice to recommend TBE vaccination for all visitors of endemic areas is inappropriate. Implementation of the risk strategy is compromised by the fact that many at-risk travellers are unaware of the risk, thus they will not consult competent health professionals. Others may consult late, and in some countries of origin no TBE vaccine is marketed.