How the immune system ages
Immunosenescence is the gradual remodeling and decline of immune function with age. A central feature is thymic involution: the thymus, where new T cells mature, shrinks and becomes less active from early adulthood onward, reducing the supply of naive T cells. The result is a contracted and skewed T-cell repertoire, with memory cells accumulating against past exposures and fewer fresh cells available to respond to new pathogens or vaccines.
B-cell and innate immune changes contribute too, and the pace differs between individuals based on genetics, infections, and lifestyle.
Inflammaging and its consequences
Alongside weaker adaptive responses, aging is associated with inflammaging, a chronic low-grade rise in inflammatory signaling. This smoldering inflammation is linked in research to many age-related conditions, including cardiovascular and metabolic disease and frailty, though it is one contributing factor among many rather than a sole cause. Senescent cells secreting inflammatory factors are thought to be one source.
This is general educational information, not medical advice. Concerns about immune health, infection risk, or vaccination in older age should be discussed with a qualified clinician.