FURIN and respiratory tract infectious disorder: We previously reported (15) that IM injection of MVA expressing a modified S protein with mutations that stabilized the prefusion form, inactivated the furin cleavage site, and deleted the endoplasmic retention signal induced a type 1 immune response with neutralizing antibody and CD8+IFN-γ+ T cells, and protected K18-hACE2 transgenic mice from respiratory infection with SARS-CoV-2.