Abstract
The current fight against COVID-19 is compounded by the Variants of Concern (VoCs), which can diminish the effectiveness of vaccines, increase viral transmission and severity of disease. MVC-COV1901 is a protein subunit vaccine based on the prefusion SARS-CoV-2 spike protein (S-2P) adjuvanted with CpG 1018 and aluminum hydroxide. Here we used the Delta variant to challenge hamsters innoculated with S-2P based on the ancestral strain or the Beta variant in two-dose or three-dose regimens. Two doses of ancestral S-2P followed by the third dose of Beta variant S-2P was shown to induce the highest neutralizing antibody titer against live SARS-CoV-2 of the ancestral strain as well as all VoCs. All regimens of vaccination were able to protect hamsters from SARS-CoV-2 Delta variant challenge and reduce lung live virus titer. Three doses of vaccination significantly reduced lung viral RNA titer, regardless of using the ancestral or Beta variant S-2P as the third dose. Based on the immunogenicity and viral challenge data, two doses of ancestral S-2P followed by the third dose of Beta variant S-2P could induce broad and potent immune response against the variants.
Competing Interest Statement
C. C., T.-Y. K., C.-C. W., W.-.H. T, C.-E. L., Y.-J. L., and M.-Y. L. are co-inventors for US provisional patent applications 63/240,408, 63/240,080, and 63/248,189.