The investigators plan to study the response to influenza vaccines much more broadly and deeply across different age groups and with different vaccine formulations and to probe the influence of genetics on these responses using monozygotic and dizygotic twins. On an investigational basis, investigators plan to compare various immunological responses, identify age-specific biomarkers or clusters of markers, quantify the frequency of influenza-specific T-cells pre- and post-vaccination, and determine the effective breadth of T-cell repertoire to an influenza vaccine within an individual as a function of age and to what degree this is genetically determined.~Twin Groups A-E will receive a single administration of the 2010-2011 formulation of seasonal trivalent inactivated influenza vaccine (TIV). Group F, elderly monozygotic twin participants, will be randomly assigned to receive a single dose of inactivated vaccine, either the usual dose or the High-Dose TIV. Blood samples to conduct the assays described will be taken at pre-immunization, Days 7-10 and 28 post-immunization. Each twin is counted as a single participant. All reporting numbers reflect the number of participants, not the number of twin pairs.
This study will investigate response to influenza vaccines in monozygotic and dizygotic twins of different ages.