We present compelling evidence for the existence of an evolutionary adaptive response to viral agents such as SARS-CoV-2, that results in the humanin vivobiosynthesis of a family of compounds with potential antiviral activity. Using nuclear magnetic resonance (NMR) spectroscopy, we detected a characteristic spin-system motif indicative of the presence of an extended panel of urinary and serum metabolites during the acute viral phase. The structure of eight of nucleoside analogues was elucidated (six of which have not previously been reported in human urine), and subsequently confirmed by total-synthesis and matrix spiking. The molecular structures of the nucleoside analogues and their correlation with an array of serum cytokines, including IFN-α2, IFN-γ and IL-10, suggest an association with the viperin enzyme contributing to an endogenous innate immune defense mechanism against viral infection.