• Tolerability/safety assessments (physical/neurol.exam., ECG, vital signs, standard and special immunological laboratory evaluations, MRIs, EEGs, AE/SAE monitoring). [ Time Frame: at multiple timepoints including but not limited to screening, baseline, and through the end of the study to Week 52. ]
  
• Antibody titers (IgM and IgM titers against amyloid and carrier protein). [ Time Frame: at multiple timepoints including but not limited to baseline and through the end of the study to Week 52 ]
  

• Immune response, cognitive and functional assessments [ Time Frame: at multiple timepoints including but not limited to baseline and through the end of the study to Week 52 ]
  

Inclusion Criteria:

• males and/or females patients between 50 to 80 years of age (both inclusive).
• female patients must be without childbearing potential (post-menopausal or surgically sterilized).
• diagnosis of dementia of the Alzheimer's type according to the DSM-IV criteria (Diagnostic and Statistical Manual of Mental Disorders, 4th edition).
• mild to moderate AD as confirmed by Mini-Mental State Exam score of 16 to 26 (both inclusive) at screening.
• able to provide written informed consent and having a responsible caregiver that can provide written assent prior to study participation. For patients who have been declared mentally incompetent, a legal representative will need to provide informed consent on their behalf.

Exclusion Criteria:

• previously participated in an AD vaccine study and received active treatment
• history or presence of an active autoimmune and/or cerebrovascular disease
• history or presence of seizures, with an acute or chronic inflammation
• clinically relevant atopic condition, who suffer from an other neurodegenerative disease and/or psychiatric disorders (with the exception of successfully treated depression)
• immunosuppressive treatment including systemic steroids
• obtained a vaccination (e.g. against influenza) within 4 weeks before the first study drug injection
• advanced, severe, progressive or unstable disease that might interfere with the safety of the patient
• started treatment with psychotropic medication within 3 months (4 weeks for SSRIs and other newer antidepressants without anticholinergic properties) prior to randomization with the exception of mild hypnotic drugs (e.g. zolpidem, zopiclone, oxazepam) and low doses of neuroleptic drugs (e.g. up to 2 mg risperidone).

Patients, who are on stable treatment with cholinesterase-inhibitors (ChEIs) and/or memantine for at least 3 months, and/or with SSRIs and/or other newer antidepressants (without anticholinergic properties) for at least 4 weeks before randomization, can be included into the study.