It has been reported in small studies, that people who die of severe COVID-19 showed abnormalities resembling Alzheimer’s disease. 

In a study published in Alzheimer’s and Dementia, it has been reported that defective ryanodine receptors linked to the accumulation of tau into neurofibrillary tangles that are present in Alzheimer’s disease, were also reported in high levels in the COVID-19 patient’s brains. In the study, researchers studies the brains of 10 COVID-19 patients and detected defects in proteins called ryanodine receptors that manage the passage of calcium into cells. (Feb 5, Reuters)