Risk Factors for Secondary Immunodeficiency in the Aged.

Secondary immune deficiencies, in which the immune system is weakened or compromised by another factor, have become prevalent. Secondary immune deficiencies are particularly pertinent in aged people because numerous etiologies cause immune dysfunction in this population. Immunosenescence is characterized by inflammaging, cellular senescence, thymic involution, reduced naive T- and B-cell output, restricted antigen receptor diversity, and impaired innate immune cell function, leading to increased susceptibility to infection and diminished vaccine responsiveness. Malnutrition is common in aged people and exacerbates immune dysfunction through impaired cell-mediated immunity, micronutrient deficiencies, and weakened mucosal barriers. Immunosuppressive therapies are also frequently used in older adults, such as corticosteroids, cytotoxic agents, purine analogs, and biologics. Other comorbidities such as chronic kidney and liver disease, diabetes, cardiovascular disease, chronic lung disease, and persistent viral infections also contribute to immune dysregulation. Given these cumulative risks, vaccination remains a cornerstone of prevention. Updated immunization strategies targeting COVID-19, influenza, respiratory syncytial virus, herpes zoster, and pneumococcal disease are critical to reducing morbidity and mortality in this vulnerable population.