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An infectious etiology of Alzheimer’s disease has been postulated for decades. It remains unknown whether SARS-CoV-2 viral infection is associated with increased risk for Alzheimer’s disease. In this retrospective cohort study of 6,245,282 older adults (age≥ 65 years) who had medical encounters between 2/2020–5/2021, we show that people with COVID-19 were at significantly increased risk for new diagnosis of Alzheimer’s disease within 360 days after the initial COVID-19 diagnosis (hazard ratio or HR: 1.69, 95% CI: 1.53–1.72), especially in people age≥ 85 years and in women. Our findings call for research to understand the underlying mechanisms and for continuous surveillance of long-term impacts of COVID-19 on Alzheimer’s disease.