Investigation of the Seropersistence of TBE Antibodies and the Booster Response to FSME-IMMUN 0.5 ml in Adults Aged 18 - 67 Years

Inclusion Criteria: Male and female subjects 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 third vaccination with FSME-IMMUN 0.5ml during the course of Baxter Study 213; * blood was drawn before and after their third vaccination during the course of Baxter Study 213; * they showed an ELISA-concentration \> 126 VIE U/ml and / or a NT-titer \>= 1:10 after the third vaccination in Baxter Study 213; * they agree to keep a Subject Diary. Exclusion Criteria: Subjects will be excluded from participation in this study if they: * received any TBE vaccination since their third vaccination with FSME-IMMUN 0.5ml; * received a vaccination against yellow fever and / or Japanese B-encephalitis since their third vaccination with FSME-IMMUN 0.5ml; * are known to be HIV positive (a special HIV test is not required for the purpose of the study) since their third vaccination with FSME-IMMUN 0.5ml; * have a known or suspected problem with drug or alcohol abuse (\> 4 liters wine / week or equivalent level of other alcoholic beverages); * have received a blood transfusion or immunoglobulins within one month to the first and second blood draw; * have participated in another Baxter vaccine study within the last six months (with the exception of follow-up studies). Subjects will not be eligible for booster vaccination if: * they do not meet the inclusion/exclusion …