CD4 and infection: The Sette and Crotty groups were among the first to publish data from AIM assay characterization of COVID‐19 T‐cell immunity, discovering that natural infection–induced CD4+ and CD8+ T cells have a half‐life of 3–5 months and that the magnitude of CD4+ and CD8+ T‐cell responses negatively correlates with disease severity.32, 98