APOE and Alzheimer disease: Here, we summarize the potential routes by which SARS-CoV-2 invades the CNS and then provide an overview of the associations and potential shared pathogenic mechanisms between SARS-CoV-2 and AD, with a focus on the ACE2 receptor, APOE genotype, age, and neuroinflammation, in order to advance the understanding of associations between COVID-19 and AD.