SignificanceVaccines profit from the addition of adjuvants to better and more specifically initiate, amplify, and shape immune responses. Although the number of adjuvant candidates has steadily increased, peaking in the current SARS-CoV-2 pandemic, little is known about their inherent mode of action. Using human blood immune cells, we established a multilayer method to systematically assess the adjuvants’ effects on innate and adaptive immune cells. By employing a multiplex analysis with cells from 30 different donors, we determined important patterns of adjuvant function. Moreover, we demonstrate correlates of an antiviral immune response using a Toll-like receptor 7/8 ligand adjuvant and single-stranded RNA. This knowledge about adjuvants’ distinct immune signatures supports the selection of safe and effective adjuvants for future vaccines.