SARS1 and COVID-19: We used a SARS-2 Beta library for serum from the naive and then mosaic-8b immunized animals, and a SARS-2 WA1 library for serum from animals vaccinated with an mRNA-based COVID-19 vaccine and then immunized with mosaic-8b to enable the mapping of Ab responses against an RBD matched to the first exposure (SARS-2 Beta is a matched RBD for the originally naive mice immunized with mosaic-8b; WA1 is a matched RBD for mice pre-vaccinated with WA1 spike-encoding mRNA-LNP).