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Ask a neuroscientist…

AJDC is aimed at all who work with people with dementia, including those who are new to the dementia workforce and may want to learn more about the basics of dementia. This article is part of a series by neuroscientist and AJDC Editorial Advisor Dr Lezanne Ooi, who presents short, easy-to-read answers to questions about neurological changes to the brain with dementia. In this article, Dr Ooi answers the question:

‘COVID-19 and dementia: what do we know?’

As of the end of September 2021 there have been over 88,000 cases of COVID-19 in Australia and sadly, over 1100 deaths. In the first 10 months of 2020, among the 858 Australians who died due to COVID-19, 257 people (or 30%) of them also had dementia, with most deaths occurring among those aged 85 and over (AIHW 2021).

We know that people with dementia are more likely to develop severe COVID-19 and die from the virus than people without dementia, and that they are less likely to report respiratory conditions as a result of COVID-19 (AIHW April 2021).

This article examines what is currently known about the impact of COVID-19 on the brain and on people living with dementia, and why they are more at risk of being infected.


Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus that causes COVID-19. It affects not just the respiratory system but also many other tissues of the body. SARS-CoV-2 enters cells by hijacking a protein called angiotensin converting enzyme 2 (ACE2).

ACE2 is also present in brain cells and, as such, SARS-CoV-2 is also able to enter the cells of the brain. When this happens, our immune system in the brain becomes activated in a process called neuroinflammation. Even in the absence of dementia, SARS-CoV-2 infection is associated with impaired cognition, possibly due to neuroinflammation (Toniolo et al 2021).

Originally published in the Australian Journal of Dementia Care print edition,
Vol 10 No 4, October/November/December 2021

Download the PDF version of this article


  1. Alzheimer’s Association. Coronavirus (COVID-19): Tips For Dementia Caregivers: Coronavirus (COVID-19): Tips for Dementia Caregivers | alz.org
  1. Dementia Australia (July 2020) The Impact of COVID-19 On People Living With Dementia, Families and Carers. A Submission To The Royal Commission Into Aged Care Quality and Safety: https://www.dementia.org.au/sites/default/files/2021-08/Dementia-Australia-The-impact-of-COVID19-on-people-with-dementia-and-carers.pdf
  1. Mok et al (2020) Tackling Challenges in Care of Alzheimer’s Disease and Other Dementias Amid the COVID-19 Pandemic, Now and In The Future. Alzheimer’s and Dementia 16 1571-1581: Tackling challenges in care of Alzheimer’s disease and other dementias amid the COVID‐19 pandemic, now and in the future – Mok – 2020 – Alzheimer’s & Dementia-Wiley Online Library
  1. Wang et al (2020) Dementia Care During COVID-19. The Lancet 395(10231) 1190-1191: Dementia care during COVID-19 – The Lancet

Increased risk

Dementia, and particularly Alzheimer’s disease, is associated with higher rates of infection and hospitalisation due to COVID-19 (Zhou et al 2021). So why are people with dementia more at risk from SARS-CoV-2 infection? Research is still in the early stages, however there are potentially a few reasons.

Firstly, the overwhelming majority of people living with dementia are elderly and at risk of more serious outcomes. Even when age is taken into account, people with dementia are at increased risk of having comorbidities, such as coronary artery disease, hypertension and diabetes.

A meta-analysis* of data from 10 articles representing 119,218 participants suggested that dementia comorbidities increase the risk of COVID-19 infection and mortality (Liu et al 2020). Another study showed that in locations around the world where there were more cases of dementia, these were linked with higher COVID-19 caseloads and death (Azarpazhooh et al 2020).  (*Meta-analyses look at data from multiple studies and many participants.)

A person’s risk of Alzheimer’s disease is affected by a large number of their genes. One of the major genetic risk factors for Alzheimer’s is APOE, which makes a protein called apolipoprotein E. There are three different variants of the APOE gene in the human population, and these variants are passed on from parents to their children.

Apolipoprotein E is important for transporting certain fats, such as cholesterol, into cells, a critical process for brain cell function. However, apolipoprotein E has various other important functions, in many different cell types, and the version of APOE that increases the risk of Alzheimer’s (APOE4), also increases the risk of heart disease. Initial studies from the UK suggest that APOE4 appears to lead to increased severity of SARS-CoV-2 infection, possibly due to increased neuroinflammation (Kuo et al 2020).

COVID-19 and delirium

Among people diagnosed with dementia, one of the most frequent and earliest symptoms of COVID-19 is delirium (Beach et al 2020). Delirium is a serious medical condition whereby a person’s mental ability is compromised. It affects up to 50% of elderly patients in hospital (Fong et al 2015), is often associated with poor outcomes for patients with dementia and can have significant consequences (Witlox et al 2010). The effects of respiratory failure due to SARS-CoV-2 infection can cause hypoxia (reduced oxygen availability) in the brain and this is thought to worsen cognition and increase the risk of delirium in people with dementia.


SARS-CoV-2 infection increases a number of health risks for people living with dementia, including delirium and psychiatric disturbances. Research into the reasons why this is the case is ongoing and will need to remain a priority to protect these most vulnerable members of our community.


Australian Institute of Health and Welfare (AIHW) (April 2021) Dementia Deaths During the COVID-19 Pandemic in Australia, Summary. Web report, available at: https://bit.ly/dementia-deaths-summary

Azarpazhooh MR, Amiri A et al (2020) Correlations Between COVID-19 and Burden of Dementia: An Ecological Study And Review Of Literature. Journal of Neurological Science 416 117013.

Beach SR, Praschan NC et al (2020) Delirium in COVID-19: A Case Series and Exploration of Potential Mechanisms for Central Nervous System Involvement. General Hospital Psychiatry 65 47-53.

Fong et al (2015) The Interface Between Delirium and Dementia in Elderly Adults. The Lancet Neurology 14(8) 823-832.

Kuo C-L, Pilling LC et al (2020) APOE e4 Genotype Predicts Severe COVID-19 In The UK Biobank Community Cohort. The Journals of Gerontology Series A, Biological Sciences and Medical Sciences 75(11) 2231-2232.

Liu N, Sun J et al (2020) The Impact of Dementia on the Clinical Outcome of COVID-19: A Systematic Review and Meta-Analysis. Journal of Alzheimer’s Disease 78(4)1775-1782.

Toniolo S, Scarioni M et al (2021) Management Group of the EAN Dementia and Cognitive Disorders Scientific Panel. Dementia and COVID-19, A Bidirectional Liaison: Risk Factors, Biomarkers, and Optimal Health Care. Journal of Alzheimer’s Disease 82(3) 883-898.

Witlox et al (2010) Delirium in Elderly Patients and the Risk of Postdischarge Mortality, Institutionalisation, and Dementia: A Meta-Analysis. JAMA 304(4) 443-451.

Zhou J, Liu C et al (2021) Cognitive Disorders Associated With Hospitalization of COVID-19: Results From An Observational Cohort Study. Brain, Behaviour and Immunity 91 383-392.

Dr Lezanne Ooi is a neuroscientist at the Illawarra Health and Medical Research Institute, Wollongong, and the School of Chemistry and Molecular Bioscience, University of Wollongong, NSW. To follow up with the author, email lezanne@uow.edu.au. The author is supported by a National Health and Medical Research Council (NHMRC) of Australia Boosting Dementia Research Leadership Fellowship (APP1135720)

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