The investigators and others have shown that the first influenza virus someone is exposed to leaves an immunological imprint that affects antibody responses to antigenically related influenza strains later in life. Year of birth can therefore be used to predict influenza virus exposures during the first years of life. It is possible that immune responses to influenza vaccination later in life differ between people with different birth years, depending on what virus someone was imprinted with. This could result in birth year differences in antibody responses upon vaccination and vaccine effectiveness. However, the effect of year of birth on the specificity of humoral and cellular immune responses elicited by influenza vaccination has not been studied in depth. In this study, the investigators will measure influenza virus cellular and humoral immune responses in individuals of different birth years before and after influenza vaccination.
Cellular and humoral immune responses before and after seasonal influenza vaccination will be assessed. Each year, up to 100 participants will be enrolled. To study age-specific differences in immune responses, participants with various years of birth will be enrolled. The investigators hypothesize that humans with different birth years will mount antibody and cellular responses of different specificities following seasonal influenza vaccination.