Immunization against amyloid beta (Aβ) for the treatment of dementia had high hopes, with the immunotherapy dramatically reducing Aβ levels; however, trials were halted in the early 2000s when volunteers receiving the vaccine developed meningoencephalitis. Here, Johannes Attems, MD, of Newcastle University, Newcastle, UK, discusses what has been learnt from this research, and the relationship between tau and Aβ.