ART4 and infection: To examine this hypothesis, we assessed ratiometric S glycoprotein domain specificity using an RBD competition ELISA in an early pandemic cohort (n = 13) and observed that immunological imprinting through ancestral S exposure differs between infection (with augmentation toward S2 and NTD) and vaccination (with augmentation toward RBD), and this differential antibody orientation persists in hybrid immune individuals (Figure 1A).