The objective is to confirm the optimal dose of IC43 in regard to immunogenicity, safety and tolerability.

The study will be designed as a multi-center, observer-blinded, randomized, placebocontrolled phase 1 study in healthy adult subjects of 18 to 65 years of age. A total of 160 healthy male and female subjects is planned to be enrolled and randomized in five groups receiving different dosages and formulations of IC43 or placebo.

Inclusion Criteria:

• written informed consent obtained prior to study entry
• healthy adults aged between 18 and 65 years
• no clinically relevant pathological findings in any of the investigations at the Screening visit. Minor deviations of laboratory values from the normal range may be accepted, if judged by the investigator to have no clinical relevance
• In female subjects either childbearing potential terminated by surgery or a negative serum pregnancy test during screening and the willingness not to become pregnant during the entire study period by practicing reliable methods of contraception

Exclusion Criteria:

• History of autoimmune diseases and malignancies
• Active or passive vaccination 4 weeks before and during the entire study protocol
• Use of any other investigational or non-registered drug or vaccine in addition to the study vaccine during the study period or within 30 days preceding the first dose of study vaccine
• History of severe hypersensitivity reactions and anaphylaxis
• Known hypersensitivity or allergic reactions to one of the components of the vaccine
• Clinically significant diseases as judged by the investigator
• Immunodeficiency due to immunosuppressive therapy
• A family history of congenital or hereditary immunodeficiency