Why do older adults become seriously ill from an infection more quickly?
Ageing weakens the immune system in several ways simultaneously, making infections more dangerous. Keep vaccinations up to date and discuss nutritional deficiencies with your doctor, as these additionally increase vulnerability.
The immune system of older adults works less well than that of younger adults. The two pillars of targeted immunity, namely the cells that directly attack viruses and bacteria and the cells that produce antibodies, both perform worse. As a result, infected cells are cleared less effectively and the antibody response is weaker. This makes older adults more susceptible to infections such as influenza and COVID-19, and increases the risk of a severe course.
An important mechanism underlying this is the shrinkage of the thymus, the organ where new immune cells mature. It shrinks gradually throughout life. The consequence is that fewer fresh immune cells are available to recognise new pathogens. The body therefore relies on immune cells that have already been deployed before, and these are less flexible when confronted with unfamiliar infections.
At the same time, a smouldering, chronic inflammation plays a role. Older adults have structurally higher levels of inflammatory substances in their blood. This background inflammation, also known as inflammaging, places an additional burden on the body and is associated with a more severe course of infection. Whether that inflammation is itself the cause of the vulnerability or is more a by-product of the general decline has not yet been fully clarified.
Nutrition and co-existing illnesses make the picture even more complex. More than half of older adults admitted to hospital suffer from protein or energy deficiency, and deficiencies in vitamins and minerals also occur in older adults living at home. Both further weaken the immune system. Chronic conditions such as cardiovascular disease or diabetes, and the use of multiple medications simultaneously, also contribute to this.
All of this also affects how vaccines work. Because the immune system responds more slowly and weakly, vaccines offer older adults less protection than they do younger adults. Higher doses, special additives to vaccines, or a different method of administration can improve the response, but do not fully resolve the underlying problem.
This answer is based on several review studies that summarise existing research. The associations between ageing of the immune system and increased susceptibility to infection are broadly supported and are well grounded in biology. For inflammaging, the association with severe infection outcomes is clear, but cause and effect have not yet been fully disentangled.
Why are older adults more susceptible to influenza?
Older adults are more susceptible to influenza due to a combination of an ageing immune system, chronic diseases, and low-grade background inflammation. Ask your doctor or pharmacist whether, as someone aged 65 or over, you can receive a high-dose influenza vaccine, as it offers better protection than the standard formulation.
Does your immune system really weaken as you get older, and can you do anything about it?
Your immune system demonstrably weakens with age, but eating healthily and exercising can reduce the smouldering inflammation that accompanies it. It is still too early to rely on drugs targeting senescent cells.
Can too little sleep make you more susceptible to infections?
Too little sleep demonstrably makes your immune system more vulnerable, including to infections and vaccinations. Make sure you get sufficient sleep, even though the exact numbers and thresholds are not yet precisely known.
Why do you get sick more often when you are on a diet?
A low-calorie diet can weaken your immune system through deficiencies in minerals such as magnesium, disrupted gut bacteria and suppressed immune responses. When dieting, pay attention to adequate micronutrient intake to limit this risk.
Does your immune system really weaken as you get older?
Your immune system demonstrably weakens with age, but vaccinations remain worthwhile and a good diet can limit further decline.
Why do some people experience symptoms for months after an infection?
After an infection, multiple biological processes can continue to smoulder simultaneously, but which mechanism plays the leading role in any given individual cannot yet be predicted or specifically treated.