Over a lifetime, the burden of infectious disease - and particularly persistent infections such as cytomegalovirus - influences the pace of aging via its detrimental impact on immune function in later life. The slow upward trend in life expectancy over the past two centuries is due in no small part to reductions in infectious disease that accompanied improvements in sanitation and then medicine. In addition, in old age, once the immune system declines into ineffectieness, infectious disease becomes a much more serious concern. Infections that a young person defeats with ease become life-threatening. The primary strategy to address this issue presently adopted by the research community is to expand and improve on vaccines for older people, as the authors of today's open access paper outline. The issue with this approach is that the aged immune system is ineffective, and thus while there are some techniques that can improve vaccine performance, that performance is always going to be poor.
If we want older people to exhibit a much lower burden of infectious disease, and to respond well to vaccines, the only viable way forward is to rejuvenate the immune system. Forms of therapy that might achieve this goal include regrowth of the thymus, the organ responsible for the maturation of T cells of the adaptive immune system, and which atrophies near entirely by age 50 or so. Additionally, damaged and dysfunctional hematopoietic stem cell populations of the bone marrow must be restored to a youthful capacity to generate immune cells. Further, growing populations of exhausted, senescent, and misconfigured immune cells must be selectively destroyed. Development of each of these approaches is a major undertaking, even given that meaningful inroads have been made towards a basis for therapies.
People at an older age mainly die of three causes, accounting for 85% of them: cardiovascular disease, cancer, and respiratory system diseases. Although infection constitutes only a secondary cause of death in that group, happening mainly during the winter periods because of influenza infection and pneumonia disease, it is a major threat for aging adults in cluster environments like rest homes or health care facilities. People from that age group arriving in hospitals with a secondary diagnosis of infection monopolize the beds for a long period, recover badly and remain weak when leaving the health care facility. This results in a long-term poor overall health condition with a high cost for society.
Healthcare systems will have to deal with increasing numbers of ageing adults with severe infections, not only because of the higher number of individuals living longer but also because of the decline in their immune response, called immunosenescence, which makes them more vulnerable to pathogens. Ageing adults may thereby also become a new source of infection. However, an effective medical act to safeguard individuals and populations against infectious diseases is vaccination, which has proven its effectiveness in children and young adults. The ambition is to achieve a similar level of infectious disease control in ageing adults. This would be fundamental for enhancing healthy ageing. However, many recommended vaccines for ageing adults do not maintain an effective and/or sustained immune response, as is the case for influenza, pneumococcal disease or pertussis, for example.
Therefore, there is a need to better understand the aetiology of the major infectious diseases affecting this population. There is also a need to decipher the mechanisms underlying immunosenescence, which should lead to improved vaccine effectiveness and to the development of more efficient vaccination strategies for this age group (whom to vaccinate, when, where, how frequently, and at what price). Finally, there is a need to provide dedicated educational programs to healthcare professionals. Over the next decade, local decision makers will need to have a clear view on this healthcare problem, with access to effective tools to manage the growing healthcare burden they need to control.