Preclinical evaluation of a COVID-19 vaccine candidate based on a recombinant RBD fusion heterodimer of SARS-CoV-2

Current COVID-19 vaccines have been associated with a decline in infection rates, prevention of severe disease, and a decrease in mortality rates. However, SARS-CoV-2 variants are continuously evolving, and development of new accessible COVID-19 vaccines is essential to mitigate the pandemic. Here, we present data on preclinical studies in mice of a receptor-binding domain (RBD)-based recombinant protein vaccine (PHH-1V) consisting of an RBD fusion heterodimer comprising the B.1.351 and B.1.1.7 SARS-CoV-2 variants formulated in SQBA adjuvant, an oil-in-water emulsion. A prime-boost immunisation with PHH-1V in BALB/c and K18-hACE2 mice induced a CD4(+) and CD8(+) T cell response and RBD-binding antibodies with neutralizing activity against several variants, and also showed a good tolerability profile. Significantly, RBD fusion heterodimer vaccination conferred 100% efficacy, preventing mortality in SARS-CoV-2 infected K18-hACE2 mice, but also reducing Beta, Delta and Omicron infection in lower respiratory airways. These findings demonstrate the feasibility of this recombinant vaccine strategy.

Automated summary

Current COVID-19 vaccines have shown effectiveness in reducing infection rates, severe disease, and mortality. However, due to the continuous evolution of SARS-CoV-2 variants, the development of new accessible vaccines is necessary. This study presents preclinical data on a recombinant protein vaccine, PHH-1V, which was effective in inducing immune responses and preventing mortality in mice infected with SARS-CoV-2 variants.