New data: The study was terminated based on new efficacy data from another study

The purpose of this study is to study the effect of monthly dosing with a single dose of Lu AF20513, with and without booster vaccine, on antibody response.

Cohort 1 encompasses 8 patients enrolled prior to the Protocol Amendment (PA) 1, dose regimen 1.

Cohort 2 includes patients enrolled under the PA and will consist of 20 patients, randomly assigned to two arms:

• dose regimen 2: 10 patients who will receive one administration of booster vaccine 4 weeks prior to the first IMP administration
• dose regimen 3: 10 patients who will not receive a booster vaccine

After the PA1, the study consists of the following periods:

• Screening Period - up to 12 weeks
• Priming period: 28 weeks, monthly dosing with Lu AF20513
• Maintenance Period - 56 weeks, quarterly dosing with Lu AF20513
• Follow-up Period - 4 weeks

Inclusion Criteria:

• The patient has a diagnosis of AD or Mild Cognitive Impairment (MCI) due to AD.
• The patient has evidence of an abnormal amyloid and tau status, consistent with AD, by means of a positive CSF test at screening
• The patient is aged ≥50 and ≤85 years. If a woman, the patient must be post-menopausal.

Exclusion Criteria:

• The patient has participated in a clinical study where he/she has received passive or active anti-Aβ immunotherapy or other active immunisation for the treatment of AD.
• The patient has, in the investigator's opinion, evidence and/or history (clinically or on MRI) of any clinically significant neurodegenerative disease, serious neurological disorder, other intracranial or systemic diseases or conditions resulting in a definite or probable diagnosis of Major or Mild Neuro-Cognitive disorder other than AD, per DSM-5® criteria.

Other in- and exclusion criteria may apply