Immune response to influenza vaccination in a large healthy elderly population.

Elderly individuals not only demonstrate a greater risk of morbidity and mortality from influenza than the young, but also have greater difficulty mounting a protective response to influenza vaccine. The mechanism of the decreased efficacy of influenza vaccination in the elderly is not well understood. The present study was designed to assess the interaction between cell-mediated and humoral immune responses to influenza vaccine in a large population (n = 233) of healthy elderly individuals (mean age = 80.7) living in six continuing care retirement communities (CCRCs). While influenza vaccination resulted in significant increases in the mean anti-influenza antibody titres and mean proliferative responses of peripheral blood mononuclear cells to purified subvirion trivalent influenza vaccine one month after vaccination, only 48.9% and 30.0% of subjects had intact humoral and cell-mediated immune responses, respectively. No association was observed between intact cell-mediated and humoral responses: 14.7% of subjects had an intact cell-mediated, but not humoral response, and 32.6% of subjects had an intact humoral, but not cell-mediated response. However, IFNgamma production was significantly correlated with both antibody and cell-mediated responses to influenza vaccination, a finding not previously reported in the elderly. These results indicate that there is considerable heterogeneity among immune responses of the elderly to influenza vaccination. This heterogeneity needs to be a major consideration in evaluation of new vaccine preparations.