Methods and combination therapties for treating, preventing, and/or delaying the onset and/or development of Alzheimer's disease using an anti Aβ protofibril (such as, for example, BAN2401) and N-[3-((4aS,5R,7aS)-2-amino-5-methyl-4a,5,7,7a-tetrahydro-4H-furo[3,4-d][1-,3]thiazin-7a-yl)-4-fluorophenyl]-5-difluoromethylpyrazine-2-carboxamide and/or a pharmaceutically acceptable salt thereof (Compound X) are provided.