Abstract
While mRNA vaccines have been effective in combating SARS-CoV-2, the waning of vaccine-induced antibody responses and lack of vaccine-induced respiratory tract immunity contribute to ongoing infection and transmission. In this work, we compare and contrast intranasal (i.n.) and intramuscular (i.m.) administration of a SARS-CoV-2 replicon vaccine delivered by a nanostructured lipid carrier (NLC). Both i.m. and i.n. vaccines induce potent systemic serum neutralizing antibodies, bone marrow-resident immunoglobulin G-secreting cells, and splenic T cell responses. The i.n. vaccine additionally induces robust respiratory mucosal immune responses, including SARS-CoV-2-reactive lung-resident memory T cell populations. As a booster following previous i.m. vaccination, the i.n. vaccine also elicits the development of mucosal virus-specific T cells. Both the i.m.- and i.n.-administered vaccines durably protect hamsters from infection-associated morbidity upon viral challenge, significantly reducing viral loads and preventing challenged hamsters from transmitting virus to naive cagemates. This replicon-NLC vaccine's potent systemic immunogenicity, and additional mucosal immunogenicity when delivered i.n., may be key for combating SARS-CoV-2 and other respiratory pathogens.