IL15 and COVID-19: Furthermore, our findings confirm the applicability of an innate serum protein signature, composed of IL-15, IL-6, TNF-α, IFN-γ, CXCL10 and extended to PTX3, that might act as an early indicator of vaccine-induced protection not only in COVID-19 vaccination but also in the simultaneous immunization of COVID-19 and flu vaccines, even to T2D subjects.