A Study to Confirm Safety and Efficacy of Lecanemab in Participants With Early Alzheimer's Disease

This study will be conducted to evaluate the efficacy of lecanemab in participants with early Alzheimer's disease (EAD) by determining the superiority of lecanemab compared with placebo on the change from baseline in the Clinical Dementia Rating-Sum of Boxes (CDR-SB) at 18 months of treatment in the Core Study. This study will also evaluate the long-term safety and tolerability of lecanemab in participants with EAD in the Extension Phase and whether the long-term effects of lecanemab as measured by the CDR-SB at the end of the Core Study is maintained over time in the Extension Phase. Extension Phase Part B will continue dosing with lecanemab in countries where lecanemab may not be commercially available.

All administrations of study drug will be administered in the clinic or in the home; However, home administrations of intravenous (IV) study drug will be allowed per sponsor approval according to country and local guidelines during the COVID-19 pandemic and following its resolution, where permitted.