Humoral and cellular immune response to influenza virus vaccination in aged humans

Aging is characterized by an increased susceptibility to infectious diseases; influenza virus infection, which is easily managed by an intact immune system, represents a life-threatening disease in aged subjects. We studied 18 healthy aged subjects (> 65 years of age), vaccinated yearly with conventional anti-influenza vaccine, and 9 healthy young volunteers (mean age 26 years), without previous anti-influenza vaccination, who were vaccinated with the conventional trivalent 1990 anti-influenza preparation. Six out of the 18 aged individuals received a second boost of the same vaccine about 4 months later. In all subjects, we analyzed the humoral response to type A and B influenza viruses and the influenza type A virus-specific CTL generation. Among the elderly population with a single vaccination, 6 and 5 subjects seroconverted against type A and type B influenza virus respectively. Young subjects seroconverted in 5 cases against type A, and in 5 cases against type B influenza virus. Seroconversion took place after the second vaccination in only one subject, and the antibody production was type A specific. Influenza type A virus-specific CTL activity was significantly lower in aged subjects, compared with the values observed in the young volunteers (p = 0.017). The second vaccination partially restored this immunological impairment. These data clearly demonstrate that the elderly do not have the same ability as younger subjects to mount an antibody response, and generate influenza type A virus-specific CTL after conventional anti-influenza vaccination. Moreover, a double anti-influenza vaccination generates CTL activity levels comparable to young subjects, although it does not seem to substantially modify the antibody production.