Design and immunogenicity evaluation of pan-recombinant vaccines based on the consensus sequence of severe acute respiratory syndrome coronavirus-2 spike protein

Although multivalent vaccines are being developed to address the rapid mutations of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), universal vaccines are needed to protect against evolving variants and seasonal epidemics. We designed and evaluated the efficacy of three universal SARS-CoV-2 recombinant vaccine candidates based on a consensus sequence of spike protein from multiple variants. The candidates were designed with specific substitutions, including S-GSAS/6P and S-R/x2, to enhance immunogenicity by stabilizing the prefusion spike-protein conformation. Using murine models, we assessed humoral and cellular immune responses, protective efficacy, and viral load reduction following immunization and challenge with the ancestral and XBB1.5 strains. The pan-COVID-19 vaccine candidates stimulated the production of cytokines, specifically interferon-γ and interleukin-2, and induced neutralizing antibodies targeting the ancestral, Delta, and Omicron variants. Vaccination reduced viral replication rates in pulmonary tissues of mice infected with the ancestral and XBB1.5 variants; however, their protective efficacy varied among formulations. Candidates containing the S2 subunit elicited better immune responses and protective effects than those containing solely the S1 subunit, consistent with published evidence supporting the cross-reactivity of the S2 region. The proposed vaccine candidates represent promising broad-spectrum protective agents against rapidly mutating SARS-CoV-2 variants.