The role of cell-mediated immunity after influenza vaccination of healthy elderly individuals
Authors:   , Bernstein Erica D. , Murasko Donna 
Published: July 2024

Influenza vaccination is less efficacious in the elderly than in the young. While the efficacy of influenza vaccine is estimated to be between 70% and 90% in young adults when the vaccine strain closely resembles the epidemic strain antigenically, it is much lower in elderly nursing home patients. Even in healthy elderly vaccination results in a risk reduction of only 50% among subjects aged 60 years or older at low risk for influenza. Many vaccinated elderly demonstrate a decreased antibody response against influenza immunization, which may account for the decreased efficacy. While hemaggutination inhibition (HI) antibody titers [greater than or equal to]40 are considered protective In young subjects, several studies have shown that at least 25% of the elderly, including those who are healthy and ambulatory, do not develop HI antibody titers [greater than or equal to]40 in response to vaccine. Further in the elderly, antibody responses that are equal in magnitude to the young may not provide the same level of protection from influenza. Gravenstein and colleagues showed that of 72 vaccinated elderly who were later confirmed to have influenza infection, 60% had titers [greater than or equal to]40 and 31% had titers [greater than or equal to]640 four weeks after vaccination. This suggests that levels of antibody considered predictive of protection in young are not necessarily predictive of protection in the elderly. The high proportion of immunized elderly who develop influenza is undoubtedly related, at least in part, to the low rate of protective levels of humoral immunity following immunization. The role of cell-mediated immunity in protecting aging humans from influenza infection and its sequelae is not fully understood. Although T cells cannot prevent infection of host cells, T cell responses in both humans and mice are correlated with recovery from symptoms or with decreased viral shedding. Since the most consistent and dramatic effect of age upon the immune response is the decrease in T cell response, the increased susceptibility of the elderly to influenza infection may be related to the lack of development of influenza specific T cell responses. To evaluate the role of cell-mediated and humoral immunity in the age-related decline in influenza vaccine efficacy, we evaluated the humoral and cell-mediated responses to influenza vaccination of a large population of independently living, healthy elderly adults (N [greater than or equal to] 233). Antibody and cell-mediated responses to influenza vaccine were assessed before immunization and four weeks after vaccination over the course of three influenza seasons (1993-1996). Young controls were included in two of the study years. Our data indicate that in this population of healthy elderly, immune responsiveness after influenza vaccination is low in both the humoral and the cell-mediated arms of the immune system. with the greatest defect seen in cell-mediated Immunity. While influenza vaccination was able to significantly increase cell-mediated and humoral responses in the elderly in all years of the study, immunization was unable to rescue the response to that of young controls. Further, while there was no association between cell-mediated and humoral responses to influenza immunization, IFN[gamma] production in response to influenza vaccine was correlated with both antibody and cell-mediated responses to vaccination.