Influenza vaccine-mediated protection in older adults: Impact of influenza infection, cytomegalovirus serostatus and vaccine dosage

Abstract

Age-related changes in T-cell function are associated with a loss of influenza vaccine efficacy in older adults. Both antibody and cell-mediated immunity plays a prominent role in protecting older adults, particularly against the serious complications of influenza. High dose (HD) influenza vaccines induce higher antibody titers in older adults compared to standard dose (SD) vaccines, yet its impact on T-cell memory is not clear. The aim of this study was to compare the antibody and T-cell responses in older adults randomized to receive HD or SD influenza vaccine as well as determine whether cytomegalovirus (CMV) serostatus affects the response to vaccination, and identify differences in the response to vaccination in those older adults who subsequently have an influenza infection. Older adults (≥65years) were enrolled (n=106) and randomized to receive SD or HD influenza vaccine. Blood was collected pre-vaccination, followed by 4, 10 and 20weeks post-vaccination. Serum antibody titers, as well as levels of inducible granzyme B (iGrB) and cytokines were measured in PBMCs challenged ex vivo with live influenza virus. Surveillance conducted during the influenza season identified those with laboratory confirmed influenza illness or infection. HD influenza vaccination induced a high antibody titer and IL-10 response, and a short-lived increase in Th1 responses (IFN-γ and iGrB) compared to SD vaccination in PBMCs challenged ex vivo with live influenza virus. Of the older adults who became infected with influenza, a high IL-10 and iGrB response in virus-challenged cells was observed post-infection (week 10 to 20), as well as IFN-γ and TNF-α at week 20. Additionally, CMV seropositive older adults had an impaired iGrB response to influenza virus-challenge, regardless of vaccine dose. This study illustrates that HD influenza vaccines have little impact on the development of functional T-cell memory in older adults. Furthermore, poor outcomes of influenza infection in older adults may be due to a strong IL-10 response to influenza following vaccination, and persistent CMV infection.

Keywords: Antibody; Cytokine; Cytomegalovirus; Influenza; Older Adult; Vaccination.

Fig. 1

Comparison of antibody and cellular responses between older adults receiving HD influenza vaccine (n = 50) and older adults receiving SD influenza vaccine (n = 49) at 4 time points: pre-vaccination (week 0) and 4, 10 and 20 weeks post-vaccination. (a–c) Serum GMT for 3 influenza strains (A/H1N1, A/H3N2 and B). Error bars denote 95% CI. Significant differences between groups at a single time point determined using 2-sided Mann-Whitney test. Geometric mean iGrB response in PBMCs challenged with influenza A/H3N2 (d) and B (e). Significant difference between groups determined by ANCOVA. Error bars denote 95% CI. (f–h) Mean cytokine levels (TNF-α, IFN-γ and IL-10) in supernatants of ex vivo live influenza virus-challenged PBMCs (A/H3N2). Error bars denote SEM. Significant differences between groups at a single time point determined using 2-sided Mann-Whitney test. Significance between groups across the 4 time points was determined by ANOVA. (i) Mean IFN-γ:IL-10 ratio in supernatants of ex vivo live influenza virus-challenged PBMCs (A/H3N2). Error bars denote SEM. Significant differences between groups at a single time point determined using 2-sided Mann-Whitney test. *, p ≤ 0.05; **, p ≤ 0.01.

Fig. 2

Comparison of antibody and cellular responses between Flu⁻ older adults (n = 99) and Flu⁺ older adults (n = 7) at 4 time points: pre-vaccination (week 0) and 4, 10 and 20 weeks post-vaccination. (a–c) Serum GMT for 3 influenza strains (A/H1N1, A/H3N2 and B). Error bars denote 95% CI. Significant differences between groups at a single time point determined using 2-sided Mann-Whitney test. Geometric mean iGrB response in PBMCs challenged with influenza A/H3N2 (d) and B (e). Error bars denote 95% CI. (f–h) Mean cytokine levels (TNF-α, IFN-γ and IL-10) in supernatants of ex vivo live influenza virus-challenged PBMCs (A/H3N2). Error bars denote SEM. Significant differences between groups at a single time point determined using 2-sided Mann-Whitney test. (i) Mean IFN-γ:IL-10 ratio in supernatants of ex vivo live influenza virus-challenged PBMCs (A/H3N2). Error bars denote SEM. *, p ≤ 0.05; **, p ≤ 0.01, ***, p ≤ 0.001, ****, p ≤ 0.0001.

Fig. 3

Comparison of antibody and cellular responses between CMV seronegative older adults (CMV⁻, n = 43) and CMV seropositive older adults (CMV⁺, n = 56); at 4 time points: pre-vaccination (week 0) and 4, 10 and 20 weeks post-vaccination. (a–c) Serum GMT for 3 influenza strains (A/H1N1, A/H3N2 and B). Significance between groups at a single time pointed determined using 2-sided Mann-Whitney test. Error bars denote 95% CI. (d) Geometric mean bGrB in non-stimulated T-cells in young adults (n = 19) and CMV⁻ and CMV⁺ older adults. Error bars denote 95% CI. Significant differences were determined using t-test. (e) Geometric mean iGrB response in PBMCs challenged with either influenza A/H3N2 (black line) or B (grey line). Significance between groups across the 4 time points was determined by ANOVA. Error bars denote 95% CI. (f–h) Mean cytokine levels (TNF-α, IFN-γ and IL-10) in supernatants of ex vivo live influenza virus-challenged PBMCs (A/H3N2). Error bars denote SEM. Significance between groups across the 4 time points was determined by ANOVA. (i) Mean IFN-γ:IL-10 ratio in supernatants of ex vivo live influenza virus-challenged PBMCs (A/H3N2). Error bars denote SEM. *, p ≤ 0.05; **, p = 0.01; ****, p ≤ 0.001.