CD55 and infection: We showed that DelNS1-RBD4N-DAF LAIVs expressing various RBDs derived from variants of SARS-CoV-2 are immunogenic and able to induce both systemic and mucosal specific immunity against SARS-CoV-2 RBD and effectively protect, and in some instances cross-protect, against infection by SARS-CoV-2 variants in mouse and hamster models (Figs. 1–5 and Fig. S1–S6).