Influenza vaccine effectiveness in aged individuals: The role played by cell-mediated immunity

Older adults are particularly vulnerable to influenza virus, which continues to have a considerable impact worldwide. This is partly due to a waning immune system that attenuates the ability to respond to influenza virus and/or influenza vaccination. According to recent immunogenicity and clinical studies it is becoming increasingly clear that components other than humoral-mediated immunity are required to confer long-term protection in this population. While the level of circulating anti-hemagglutinin antibody is the gold standard used to evaluate influenza vaccine efficacy, T-cell responses appear to be a better correlate of influenza vaccine protection in the elderly population. This review gives further considerations to the age-related changes that influence the immune system's capacity to respond to influenza vaccination, focusing mainly on the impact of cell-mediated immunity, which is the component of the immune system most affected by immunosenescence.