Explainer: Why are the elderly more vulnerable to COVID-19?

In response to a report from the Office for National Statistics, stating that pensioners are 34 times more likely to die of COVID-19 than those of working age, Dr Marina Ezcurra, Lecturer in the Biology of Ageing at the School of Biosciences explains why age is such a major factor.

‘The COVID-19 pandemic sweeps across the world; elderly adults are at higher risk of getting seriously ill and dying from COVID-19. People with COVID-19 can be divided into three groups: people that do not have any symptoms, people with milder symptoms who do not require hospitalisation and people with severe respiratory symptoms and high viral load. One of the biggest unanswered questions is why some develop severe disease, whilst others do not. The current understanding is that age, frailty, chronic disease and physiological factors all play a role.

1. Ageing of the immune system

‘In general, the infection triggers a strong primary immune response in younger adults, which clears the infection. An immunity memory is also formed so that the same response is triggered quickly if there are later infections. In older adults the initial immune response is less robust, meaning there is an incomplete clearance of the infection and also the memory is weaker. This is because as the immune system undergoes dramatic age-related changes. As it ages, it declines to a state of ‘immunosenescence, losing the ability to protect against infections. Vaccines are typically less effective in older individuals because of this decline.

‘Another important aspect of ageing is that other parts the immune system become overactive. Inflammatory responses mediated by the innate immune system gain in intensity and duration, making older individuals susceptible to tissue-damaging immunity and inflammatory disease.

2. ‘Cytokine storm’: the body’s response to infection goes into overdrive

‘The decreased ability to respond to pathogens in combination with an overactive inflammatory response seems to play an important role in those who get seriously ill with COVID-19. Initially the virus spreads more easily, causing damage to the cells infected by the virus, in particular cells in the respiratory tract. The damaged cells release a form of signalling molecules called cytokines, triggering an inflammatory response.

‘In some patients, excessive or uncontrolled levels of cytokines are released which then activate more immune cells, resulting in hyperinflammation. This overreaction of the immune system, the ‘cytokine storm’, can seriously harm or even kill the patient.

3. The sudden crash in patients with COVID-19

‘The cytokine storm is a runaway response that can cause more damage to the body’s own cells than to the virus it’s trying to defeat, and is thought to be the main reason for why patients can very rapidly deteriorate. Cytokine storms might explain why some people have a severe reaction to COVID-19 while others only experience mild symptoms.

‘If the ‘air sacs’, tiny extensions of the lungs where oxygen is absorbed and carbon dioxide released, become inflamed, there is an outpour of inflammatory material (fluid and inflammatory cells) into the lungs and we end up with pneumonia. Lungs that become filled with inflammatory material are unable to get enough oxygen to the bloodstream, reducing the body’s ability to cycle oxygen and carbon dioxide. This is the usual cause of death in COVID-19 patients with severe pneumonia.

4. The importance of healthy ageing for fighting infectious diseases

‘Ageing is characterised by processes of decline typically observed across most species. These processes contribute to immune ageing and chronic inflammation, which could explain why the elderly are vulnerable to COVID-19. In addition, chronic illnesses increase the risk of severe COVID-19. Studies show that additional diseases are present in many patients, obesity, hypertension diabetes and coronary heart disease being common. These are all age-related, inflammatory diseases, and are likely to contribute to COVID-19 vulnerability.

‘To improve the ability of the population to respond appropriately to COVID-19 and other infections, it is important that we improve overall health and decrease chronic, age-related diseases. By targeting ageing we can make the body more resilient and able to withstand infections.’

Dr Marina Ezcurra, School of Biosciences, University of Kent

Dr Ezcurra is Lecturer in the Biology of Ageing. Her current research focuses on how host-microbiome interactions affect host ageing and is funded by The Wellcome Trust and Royal Society. Marina Ezcurra is a trustee board member of The British Society of Research on Ageing.