IL-15 is being used in trials for cancer and autoimmunity to increase NK cell and CD8+ T cell numbers20; however no trials are underway at the time of the writing to indicate using IL-15 with vaccines against SARS-CoV-2, despite transient increases of circulating IL-15 levels early after boost being a potential prognostic indicator of mRNA vaccine-mediated effective humoral immune response to SARS-CoV-221. Here, IL15 is linked to cancer.