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.
Older adults face a much greater risk of hospitalisation and death from influenza than younger adults. They bear the largest share of influenza-related mortality worldwide. This is not the result of a single cause, but of an interplay between changes in the immune system, chronic diseases, and the ageing of organs.
A central cause is that the immune system produces fewer new, inexperienced immune cells as we age. The thymus, the organ that matures young immune cells, shrinks considerably with age. As a result, the repertoire narrows: the body is less able to recognise new influenza variants. At the same time, so-called T-helper cells, which coordinate the immune response, function less effectively. They develop more slowly into the subgroups needed to clear the virus. The consequence is that the virus remains active for longer and inflammation in the lungs persists for longer.
In older adults, influenza is also more frequently accompanied by a lingering, low-grade inflammation throughout the body, sometimes referred to as 'inflammaging'. This chronic background inflammation is further amplified by influenza and can cause damage to the heart, kidneys, liver, and muscles. Damaged lungs also provide a favourable environment for a secondary bacterial infection, a dangerous complication to which older adults are particularly vulnerable.
Chronic conditions such as diabetes, heart failure, and lung disease also play a role: most people aged 65 and over have several of these simultaneously, and influenza and pre-existing conditions reinforce one another. This is an association, not a demonstrated causal mechanism, but the contribution to more severe illness is consistently observed.
Vaccination helps, but less effectively than in younger people: because of the ageing immune system, fewer protective antibodies are produced following a standard influenza vaccine. A vaccine with a higher antigen dose has been shown to be safer and more effective in older adults than the standard vaccine, and was developed specifically to compensate for this shortfall. If you are 65 or older, it is therefore worth asking your doctor or pharmacist whether you are receiving a high-dose formulation.
This answer draws on multiple review studies by experts in the fields of infectious diseases and immunology in older adults. The mechanisms underlying the ageing immune system are well documented and consistently described. The association between chronic diseases and influenza complications is based on observed correlation, not on controlled experiments. The evidence regarding the reduced vaccine response and the added value of high-dose vaccines is stronger, although those findings are also largely based on reviews of prior research.
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.
Does the flu shot work less well as you get older?
The flu shot demonstrably works less well in older adults than in younger people, but high-dose and other improved vaccines substantially reduce that disadvantage. Ask your doctor or pharmacist whether you qualify for such an improved vaccine.
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.
Does your immune system really weaken as you get older?
Your immune system does indeed weaken as you get older, but how quickly that happens varies considerably from person to person. Lifestyle factors play a role in this, although little has yet been proven specifically for humans.
Does spending more time outdoors help your immune system as you get older?
Spending more time outdoors may support your immune system as you get older, mainly through improved vitamin D production, but whether this actually leads to less illness has not yet been conclusively demonstrated. How polluted the outdoor air is also matters: in areas with serious air pollution, being outside can in fact be detrimental.
Which vaccinations belong to healthy ageing?
For healthy ageing, the flu vaccine (high dose), the pneumococcal vaccine, the shingles vaccine, and the RSV vaccine are well supported for people aged 60 and older; discuss which ones you are still missing with your GP or pharmacist.