Bivalent SARS-CoV-2 spike immunization with non-replicative antibiotic resistance-free DNA vaccine induces immunity to multiple virus variants.

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), the cause of the COVID-19 pandemic, continues to evolve, with new variants still causing mortality in vulnerable populations. Developing vaccines that induce immunity against multiple variants and can be rapidly adapted is key to address future threats. In this study, we assessed the immunogenicity and protective efficacy of a non-replicative antibiotic resistance-free DNA vaccine (pPAL) expressing the stabilized spike proteins from the Wuhan and Omicron variants, as well as the conserved nucleoprotein. K18-hACE2 mice received a prime-boost-boost vaccination with three pPAL plasmids encoding the Wuhan spike, Omicron spike, or Wuhan nucleoprotein. The vaccine induced antibody responses against recombinant receptor-binding domains from both spike protein variants and promoted a Th1 bias immune response, as indicated by increased IgG2a/c levels compared to IgG1. Neutralization antibodies were generated against both SARS-CoV-2 variants. Furthermore, vaccinated mice were protected from a lethal challenge with the Wuhan isolate, showing reduced viral replication in target organs. This study presents a DNA vaccine platform capable of expressing multiple SARS-CoV-2 antigens and inducing robust immunity against different viral variants. This approach offers a promising and adaptable strategy for future SARS-CoV-2 vaccination efforts.