Memory T cell responses in seronegative older adults following SARS-CoV-2 vaccination

Generating memory T cell responses besides humoral immune responses is essential when it comes to the efficacy of a vaccine. In this study, the presence of memory T cell responses after aluminum-adjuvanted inactivated whole-virion SARS-CoV-2 vaccine (CoronaVac) in seronegative and seropositive elderly individuals were examined. CD4⁺ and CD8⁺ memory T cell proliferation and IFN-γ production capacities were evaluated. Additionally, clinical frailty scale (CFS) and FRAIL scales of the individuals were scored. CD4⁺ memory T cell responses more prominent than CD8⁺ memory T cells. In seronegative individuals, 80% of them had memory CD4⁺ and IFN-γ, whereas 50% of them had memory CD4⁺ and all of them had IFN-γ responses. Additionally, 40% of seronegative patients and 50% of seropositive patients had memory CD8⁺ responses. To sum up, humoral immune responses are not associated with memory T cell responses, and in seronegative individuals, memory T cell responses can be detected.