XK and COVID-19: Since the approval of the initial COMIRNATY and SpikeVax monovalent vaccines for SARS-CoV-2, there have been on-market multivalent mRNA vaccines as well as ongoing clinical trials for multivalent vaccines targeting multiple subtypes or variants of a single pathogen [14,15,16], including bivalent COVID-19 mRNA vaccines [14,15], multivalent influenza vaccines targeting 4 hemagglutinin (HA) [14,16] proteins and neuraminidase (NA) proteins [16,17], and combination seasonal influenza/COVID-19 vaccine targets [14,16].