The aim of this study is to investigate the immune responses following a booster immunisation with the Japanese Encephalitis vaccine in elderly subjects (above 60 years of age) in comparison to a young study group.

The condition under investigation is the naturally aging immune system. The aim of this study is to investigate the immune responses following a booster immunisation with the Japanese Encephalitis vaccine in elderly subjects (above 60 years of age) in comparison to a young study group.Testing the difference of the JEV-antibody titre increase between young and elderly adults between visit 1 (before booster vaccination) and up to visit 4 (6 months after booster vaccination).

Testing cellular immunity (cytokine production after JEV as well as TBE stimulation) on visit 1, 2 (one week after booster immunisation) and 3 between both age groups.

Testing of surface markers of different T and B cell subsets before and after JE-booster vaccination (on visit 1-3) in comparison between both age groups.

Testing TBE-antibody titres before and after JE-booster vaccination (on visit 1-4) in both age groups.

Testing CMV serology at visit 1 in both age groups.

Inclusion Criteria:

• participation in the preceeding study "IXIARO®-senescence" (EudraCTno: 2010-018630-52) without protocoll violation OR 2 documented IXIARO® vaccinations 28 days (-8/+ 30 days) apart between January 2010 and April 2014 at the age of 18 to 40 years or above the age of 60.
• good state of health including individuals with medically controlled minor underlying disease (such as hypertension, hypercholesterinemia, NIDDM)
• willingness to sign written informed consent

major Exclusion Criteria:

• Already received an booster (3rd dose) of IXIARO ®
• Vaccination with other JE vaccine (e.g. Je-vax)
• clinically manifest infection with another Flavivirus within 1 year prior study inclusion (yellow fever, Dengue fever, West Nile, TBE)
• past infection with the JEV
• vaccination against yellow fever, Dengue, West Nile within 6 months prior to study inclusion
• TBE vaccination within the last 30 days prior to study inclusion
• immunosuppressive therapy (intake>14d) within 30 days before IXIARO booster till V3 (day 42+/-4), Corticosteroids like Prednisolon > and = 20mg/day; allowed: topic or inhalative application
• immunodeficiency or st. p. organ transplantation
• autoimmune disease except vitiligo or diseases of the thyroid gland with thyroid hormon substitution therapy
• immuntherapy within 2 weeks before or after Ixiaro Booster
• current acute infection or exacerbation of a chronic illness
• cancer within the last 5 years
• clinically significant haematological, renal, pulmonary, hepatic, neurological, cardiovascular disease which is not treated adequately within 12 weeks before Ixiaro booster
• known infection with HIV, Hep B and Hep C
• Guillain - Barré- Syndrome (GBS) - anamnestic
• anamnestic anaphylaxie, atopy oder severe hypersensivity against ingredients of IXIARO
• drug abuse/alcohol abuse
• pregnancy and breastfeeding
• plasma donation within the last 4 months
• receiving blood or immunglobulins within 3 months before v1
• significant mental disorder