Effect of age on cytotoxic T lymphocyte memory as well as serum and local antibody responses elicited by inactivated influenza virus vaccine.

Healthy seropositive adults aged < 40 (n = 15), 40-64 (n = 15), and > or = 65 (n = 17) years were parenterally immunized with trivalent subvirion influenza virus vaccine, and their cellular and humoral immune responses were compared. Vaccination resulted in a significant enhancement of class I human leukocyte antigen-restricted influenza A cross-reactive cytotoxic T lymphocyte (CTL) memory. Elderly subjects had significantly lower baseline and peak postvaccination mean percentages of specific lysis of influenza A virus-infected autologous targets but nonetheless mounted CTL responses to vaccine that were comparable in magnitude to those of younger adults. Serologic responses and nasal IgG responses to each of 3 vaccine strains were reduced in magnitude and frequency with advancing age. Parenteral immunization was ineffective at inducing nasal wash IgA antibodies. Between 2 and 12 weeks after vaccination, serum and nasal antibody titers decreased modestly, although the rate of decline was comparable between age groups. The ability of elderly adults to mount CTL responses after influenza vaccination suggests that T cell effector mechanisms may be an important determinant of vaccine-induced protection against serious illness in this age group.