IFNG and COVID-19: The frequencies of CD4+ and CD8+ T cells producing IFN-γ, TNF-α and IL-2 in response to SARS-CoV-2 Spike peptides were measured in randomly selected COVID-19 healthy adults ≤65 years (N=63) and frail elderly individuals >65 years (N=40) who were COVID-19 naïve at time of their first vaccination and received a three-dose mRNA vaccine schedule, 12 months after the first vaccine dose.