ABSTRACT
Background: SARS-CoV-2 vaccines capable of inducing broad and cross-reactive humoral and T cell responses help to fight against emerging variants. In this study we compared the immunogenicity and efficacy of modified vaccinia Ankara (MVA) based SARS-CoV-2 vaccine expressing furin-cleavage site inactivated stabilized spike (SdFCS) and nucleocapsid (N) delivered via intramuscular (IM), buccal or sublingual (SL) routes in rhesus macaques (RMs). Methods: Three groups (n=5/group) of RMs were immunized with MVA/SdFCS-N vaccine on weeks 0 and 4, via IM, buccal, or SL route. An additional group (control) received non-recombinant MVA via IM. IM vaccinations were delivered using needle and SL and buccal vaccinations were delivered using a needle-free injection device. All RMs were challenged with B.1.617.2 strain (Delta) of SARS-CoV-2 at week 8 via intratracheal and intranasal routes simultaneously. Various humoral and cellular immune parameters were determined post vaccination and challenge. SARS-CoV-2 subgenomic RNA (sgRNA) was measured to monitor virus replication in the upper (nose) and lower (lung) respiratory tract. Results: IM vaccination induced strong RBD-specific IgG antibody in serum, nose, throat, lung, and rectum. The serum antibody showed strong live virus neutralizing activity against WA-1/2020 (median of 415) and B.1.617.2 strains (median of 317). Serum from IM vaccinated animals also demonstrated strong non-neutralizing effector functions such as ADCD, ADCP and ADNKA. In addition, IM vaccination induced strong CD4 and CD8 T cell response in the blood that was directed against both S and N. In contrast, the SL and buccal vaccination-induced antibody showed lower neutralization titer against WA-1/2020 (143 and 302, respectively), and showed 4.5-fold lower cross reactivity neutralization titer against B.1.617.2 compared to WA-1/2020. Following challenge with B.1.617.2, the IM group RMs showed superior protection with 3 of the 5 animals being negative in upper and lower respiratory airways at Day 2. In contrast, no significant protection was observed in the SL group. Vaccine induced neutralizing and non-neutralizing antibody effector functions showed direct association with protection. Conclusion: Our findings showed that IM vaccination with improved MVA-based SARS-CoV-2 vaccine elicits cross-reactive antibody and T cell responses and protect against heterologous SARS-CoV-2 Delta challenge in RMs. They also showed IM vaccinations are superior to oral vaccinations.