What is immunosenescence, and how can it impact vaccine responses in older adults?

• A. Age-related decline in immune function leading to reduced vaccine efficacy and increased infection risk
• B. Increased immune activity with age
• C. Immunosenescence is unrelated to vaccines
• D. Immunosenescence enhances vaccine responses

Answer: (A)

Immunosenescence is the gradual decline of immune function that occurs with aging. This aging of the immune system affects both innate and adaptive responses, leading to a smaller pool of responsive immune cells and less effective signaling when needed.

In older adults, thymic involution reduces production of naive T cells, narrowing the ability to respond to new pathogens or vaccines. B cell function also changes, with less robust germinal center reactions and antibody maturation, which means lower antibody levels and sometimes antibodies that bind less effectively. All of this contributes to weaker vaccine responses: fewer people seroconvert after vaccination, the peak antibody levels are lower, and protection may wane more quickly. The situation is further influenced by chronic, low-grade inflammation (inflammaging), which can disrupt how well immune cells respond to a vaccine.

Because of these changes, vaccines may be less protective in older adults, and strategies such as higher-dose formulations, adjuvanted vaccines, or booster schedules are often used to help improve responses. The idea that immunosenescence means increased immune activity, is unrelated to vaccines, or enhances vaccine responses does not fit the reality of aging immune systems.