IFNG and infection: The rationale for using an IL-2 ELISpot assay was based on previous studies, which demonstrated that IL-2 is a highly sensitive read-out to measure SARS-CoV-2 T cells associated with protection against infection (1), and on initial experiments indicating that IL-2 and IFN-γ assays detected similar quantities of SARS-CoV-2 T cell responses.