The objective of the study is to find the optimal dose for the smallpox candidate vaccine IMVAMUNE (MVA-BN). For this purpose the study compares IMVAMUNE (MVA-BN) administered at three different dose levels.

Inclusion Criteria:

• Healthy male and female subjects, aged 18 - 30 years
• Signed informed consent after being advised of the risks and benefits of the study in a language able to understand, and prior to performance of any study specific procedure.
• Free of obvious health problems with acceptable medical history by screening evaluation and physical examination.
• Subject of not of child-bearing potential or all of the following: A urine/serum ß-HCG pregnancy test gives a negative result, use of adequate contraceptive precautions for 30 days before first vaccination.

Exclusion Criteria:

• Known or suspected history of smallpox vaccination or typical vaccinia scar.
• Positive test result in MVA specific ELISA or PRNT at screening.
• Positive result in HIV or HCV antibody test at screening.
• HbsAG positive at screening.
• Pregnancy or breast-feeding.
• Uncontrolled serious infection i.e. not responding to antimicrobial therapy
• History of any serious medical condition, which in the opinion of the investigator, would compromise the safety of the subject.
• History of autoimmune disease
• History of malignancy.
• History of chronic alcohol abuse and/or intravenous drug abuse.
• History of allergic disease or reactions likely to be exacerbated by any component of the vaccine.
• History of anaphylaxis or severe allergic reaction.
• Acute disease (a moderate or severe illness with or without a fever) at the time of enrolment.
• Any vaccinations within a period starting 30 days prior to administration of the vaccine and ending at study conclusion.
• Chronic administration of immuno-suppressants or other immune-modifying drugs.
• Administration or planned administration of immunoglobulins and/or any blood products during the study period.
• Use of any investigational or non-registered drug or vaccine.