TBE Seropersistence up to 10 Years After First Booster in Adults

Inclusion Criteria: Subjects who participated in the first and second precursor studies will be eligible for participation in this study if: * they understand the nature of the study, agree to its provisions and provide written informed consent * they received the first booster vaccination with FSME-IMMUN 0.5ml during the first precursor study and did not receive a second booster vaccination in the second precursor study * blood was drawn after their first booster vaccination in the first precursor study Exclusion Criteria: Subjects will be excluded from participation in this study if they: * received any TBE vaccination since their first booster vaccination with FSME-IMMUN 0.5ml * have a history of infection with or vaccination against other flaviviruses (e.g. dengue fever, yellow fever, Japanese B-encephalitis) since their first booster vaccination with FSME-IMMUN 0.5ml * are known to be HIV positive since their first booster vaccination with FSME-IMMUN 0.5ml * have a known or suspected problem with drug or alcohol abuse