Role of humoral and cell-mediated immunity in protection from influenza disease after immunization of healthy elderly

Abstract

While influenza immunization significantly reduces the risk of pneumonia and associated deaths, vaccination of elderly only affords 30-50% protection against influenza disease. The purpose of this study was to: (1) evaluate the consistency of immune responses across multiple years in young and elderly; (2) determine the contribution of antibody and cell-mediated responses in protection after immunization with influenza vaccine. Independently living healthy elderly (>200/year; mean age 78.8-80.6/year) were recruited yearly in this four year study. The results clearly demonstrate: (1) both young and elderly consistently produced significant antibody and T cell proliferative responses to influenza vaccine upon yearly immunization; however, both responses of elderly were significantly and consistently lower than young. (2) Percentages of both young and elderly demonstrating protective titers (i.e. HI>/=40) increased post-immunization each year, but were consistently higher in young compared to elderly. (3) The risk of developing influenza disease after immunization was highest among elderly demonstrating neither antibody nor cell-mediated responses. Importantly, the risk of influenza disease was comparable in elderly demonstrating a cell-mediated response alone, an antibody response alone, or both cell-mediated and antibody responses. This suggests that cell-mediated responses play a significant role in protection in at least a subset of elderly from influenza disease after immunization.