Vaccination of cats with Sad23L-nCoV-S vaccine candidate against major variants of SARS-CoV-2.

Cats are susceptible to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and risk transmitting viruses to naive cats or humans. Here, based on our novel adenovirus-vectored COVID-19 vaccine, the immunogenicity of Sad23L-nCoV-S vaccine was evaluated in cats by prime-boost vaccinations. Five cats were primed with a dose of 10 plaque-forming units (PFUs) Sad23L-nCoV-S vaccine and then boosted with an equal dose of same vaccine at a 4-week interval. Cat serum neutralizing antibody (NAb) titers (the sample dilution at which 50% inhibitory concentration [IC]) were measured as IC 15,849 to wild-type strain, IC 6,591 to Alpha, IC 2,315 to Beta, IC 2,744 to Gamma, IC 1,848 to Delta, and IC 318 to Omicron variants of pseudotyped SARS-CoV-2 viruses at week 6 post-prime vaccination. All NAb levels to these five variants were ≥IC 49 from vaccinated cats at week 10, while 48.8% to Delta and 100% to Omicron variants were <IC 10 from human vaccinees at week 2 or 4 after receiving two injections of the inactivated SARS-CoV-2 vaccines. Robust T cell response of interferon (IFN)-γ to S peptides were detected in vaccinated cats. It was concluded that Sad23L-nCoV-S vaccine could be a promising vaccine candidate against SARS-CoV-2 infection in cats by prime or plus boost vaccinations.