Replication-competent vaccinia virus-vectored oral vaccines provide complete protection against the SARS-CoV-2 challenge and effectively prevent viral transmission via respiratory droplets in mice and minks

• The rWR-S6P is orally immunogenic and provides complete protection against the SARS-CoV-2 challenge in mice and minks. • Oral administration of rWR-S6P effectively prevents transmission of SARS-CoV-2 among minks via respiratory droplets. • Combined vaccination with recombinant WRs is an effective administration strategy for preventing and controlling animal COVID-19. Here, we generated three recombinant replication-competent vaccinia virus (VACV) Western Reserve (WR) strains rWR-S6P, rWR-DS6P, and rWR-BA2S6P. These recombinant viruses express the prefusion-stabilized S proteins S6P, DS6P, and BA2S6P, which target the full-length S protein of the strain ancestor and variants Delta and Omicron BA.2 of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), respectively. These recombinant viruses maintained the growth property of the parental virus WR in CV-1 cells. A mouse study indicated that the insertion of these modified S genes reduced the virulence of the vector virus WR. Oral or intramuscular vaccination with rWR-S6P elicited a robust neutralizing antibody (NA) response against live SARS-CoV-2 and provided complete protection against the SARS-CoV-2 challenge in mice and minks. Of note, oral vaccination with rWR-S6P induced significantly higher titers of SARS-CoV-2 NAs and superior protective efficacy compared to intramuscular vaccination at an equivalent dose. More importantly, oral administration of rWR-S6P effectively prevents transmission of SARS-CoV-2 among minks via respiratory droplets. Furthermore, combined oral vaccination with three recombinant WRs induced a strong and long-lasting NA response against homotypic SARS-CoV-2 pseudovirus in mice without compromising their immunogenicity profiles. These findings indicate that the attenuated replication-competent VACV-vectored vaccines hold promise as effective oral COVID-19 vaccines for minks while demonstrating that combined vaccination is an effective administration strategy for preventing and controlling COVID-19.