A multicenter Phase II RAPID-PROTECTION trial reports that combining the long-acting monoclonal antibody AZD7442 with a bivalent Ancestral/BA.1 mRNA/LNP COVID-19 vaccine was well tolerated in immunocompromised adults. Investigators reported no serious adverse events across 139 participants and showed that AZD7442 serum concentrations remained detectable through day 180. Humoral responses increased after AZD7442 and again after vaccination, but functional neutralization against Omicron stayed limited. Epitope mapping suggested vaccination preferentially boosted antibodies to S2 and S1 regions not targeted by AZD7442, while also increasing S2-specific memory B cells. The trial’s pattern of cross-reactive T-cell responses supported consideration of combined antibody-and-vaccine strategies for next-generation therapeutic antibody development.