T cell testing using a commercial T cell test, QuantiFERON SARS-CoV-2 RUO, offers insight into the immune response to infection and vaccination of patients with COVID-19 and suggests that age and time from infection are significant factors related to the magnitude of cell-mediated immune (CMI) responses to COVID-19. The findings are presented at ASM Microbe 2022, the annual meeting of the American Society for Microbiology.