Those that fall within this age bracket were found to be 50 to 80 per cent more at risk of developing the form of dementia than those who have not had the virus.
The findings show that the risk of Alzheimer’s disease nearly doubled from 0.35 per cent to 0.68 per cent in older people in the year following their diagnosis.
The reseachers are still unclear whether coronavirus triggers new development of Alzheimer’s disease or accelerates its emergence.
The research team analysed the anonymous health records of 6.2 million adults aged 65 and older in the United States who received medical treatment between February 2020 and May 2021.
The records of those they examined had no prior diagnosis of Alzheimer’s disease.
The researchers split the people into two groups. Those who had previously contracted Covid were placed in one group, while those who had no documented cases of the virus were separated into another.
There were more than 400,000 people in the group who had had Covid and 5.8 million in the other.
Watch: Study finds link between COVID-19, Alzheimer’s risk
Dr Pamela Davis, a research professor at the Case Western Reserve School of Medicine, and co-author of the study, said: “The factors that play into the development of Alzheimer’s disease have been poorly understood, but two pieces considered important are prior infections, especially viral infections, and inflammation.
“Since infection with Sars-CoV2 has been associated with central nervous system abnormalities including inflammation, we wanted to test whether, even in the short term, Covid could lead to increased diagnoses.”
Dr Davis added: “If this increase in new diagnoses of Alzheimer’s disease is sustained, the wave of patients with a disease currently without a cure will be substantial, and could further strain our long-term care resources.
“Alzheimer’s disease is a serious and challenging disease, and we thought we had turned some of the tide on it by reducing general risk factors such as hypertension, heart disease, obesity and a sedentary lifestyle.
“Now, so many people in the US have had Covid and the long-term consequences of Covid are still emerging. It is important to continue to monitor the impact of this disease on future disability.”
The team plans to continue studying the effects of Covid on Alzheimer’s disease and other neurodegenerative disorders.
They aim to also focus on people who may be more vulnerable and find ways to repurpose FDA-approved drugs to treat Covid’s long-term effects.
The results were published in the Journal of Alzheimer’s Disease.