 Significance: This study will provide critical information on the best technique in vaccine candidate testing and improve influenza treatment approaches. The long-term goal of this research is to identify the T-cell responses that are surrogates biomarkers of serious complications of influenza in older adults and predict vaccine efficacy prevention of influenza illness and vaccine effectiveness prevention of serious complications. Further, translating new insights into age-related immune dysfunction to the design of new influenza vaccines is critical to addressing this unmet need in the population aged 65 and older. 