Eight-hundred patients will be enrolled at approximately 50 study centers. Informed consent (i.e., from the patient or from the patient's legally authorized representative) or waiver will be obtained according to regional requirements prior to any study related procedures. Patients will be randomized to receive either IC43 100 mcg or placebo and will receive the first vaccination on Day 0. The second vaccination will be applied on Day 7. In case ICU discharge occurs before Day 7, immunization will be done at the hospital ward.