Randomized, placebo-controlled, partially blinded phase 2 pilot study. Multicenter study (approximately 50 centers) in approximately 9 countries. Proposed start date is December 2008. The study duration per patient is estimated to be 90 days. Overall study duration is estimated to be 12-18 months.

This is a randomized, placebo-controlled, multi-center, partially blinded [i.e., 100 mcg and 200 mcg IC43 with Al(OH)3,, respectively] and placebo, but unblinded for non-adjuvanted IC43 [i.e., 100 mcg w/o Al(OH)3] phase 2 pilot study. The study population consists of male or female ICU patients with a need for mechanical ventilation for more than 48 hours, aged between 18 and 80 years.

Inclusion Criteria:

• Male or female patients aged between 18 and 80 years
• Patients admitted to an ICU with a need for mechanical ventilation for more than 48 hours at visit 0
• At high risk for acquiring infection against P. aeruginosa at visit 0.
• Patients who, as determined by the investigator, have a high probability of survival for at least 48 hours.
• In females, either childbearing potential terminated by surgery or 1 year post menopausal, or a negative pregnancy test and the willingness of practicing a reliable methods of contraception
• Written informed consent or waiver according to the national regulations

Exclusion Criteria:

• Known use of any other investigational or non-registered drug within 30 days prior to IC43 vaccination at Visit 0
• Low severity of illness defined by an acute physiology score < 8 at visit 0
• Patients < 6 months post organ transplantation
• Severe thrombocytopenia or other coagulopathy which in the opinion of the investigator makes the patient unsuitable for intramuscular injection
• Pregnancy, lactation
• Persons who have been committed involuntarily to an institution, e.g. mental health facility or prison, will not participate in the study